JP3238649B2 - 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 a light intensity control 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 In an optical scanning device or the like, a light beam emitted from a light source is divided into a monitor light beam and a main light beam, the light intensity of the monitor light beam is detected, and the light intensity of the main light beam is adjusted based on the detected light intensity. For this purpose, a light intensity control device for adjusting the light emission amount of the light source is used. Taking an optical disc device as an example, a laser beam emitted from a light source such as a semiconductor laser is split by a light splitting element such as a half mirror, and one of the split beams is used as a monitor beam for light intensity detection, and the other is an image as a main beam. It is guided to an optical disk located on the surface and used for reading and writing information. The light intensity control device controls the light emission intensity of the light source so as to obtain a predetermined light intensity on the optical disk based on the light intensity of the monitor light beam, so-called APC.
(Automatic Power Control) operation. This APC
In order to perform the operation, it is necessary that the output signal intensity of the detecting means for detecting the monitor light beam and the light intensity of the main light beam have a certain correlation. However, since the reflection and transmission characteristics of the light splitting element and the subsequent optical element have polarization-dependent characteristics (polarization dependence),
When the polarization state of the light beam incident on the light splitting element changes, the balance between the output signal intensity of the monitor light and the light intensity of the main light beam is broken, and the APC operation cannot be effectively performed.

For example, in an apparatus using a plurality of light sources, the polarization states of a plurality of light beams tend to vary. Also, even if it is a light beam emitted from one light source,
Depending on the environment and the arrangement of the optical members, the polarization state can be variously changed before the light enters the light splitting element. Under the condition that the polarization state of the incident light beam is changed in this way, an accurate output signal of the monitor light cannot be obtained because the optical members including the light splitting element have polarization dependent characteristics, and the APC is operated. Even if the light emission amount of the light source is adjusted, the light intensity of the main light beam on the image plane cannot be maintained at a predetermined level. In some cases, the error of the light intensity on the image plane is rather increased by performing the APC operation.

In order to solve the above-mentioned problem, the applicant of the present invention disclosed in Japanese Patent Application No. 8-75182 using a beam splitter to convert a monitor light beam into first and second linearly polarized light components in which the vibration directions of electric field vectors are orthogonal to each other. (S-polarized light and P-polarized light), and the output of the monitor light is corrected by calculating and recombining the respective polarized components at the required addition ratio, resulting in a change in the polarization state of the light incident on the half mirror and the like. A light intensity controller and a control method for correcting the imbalance between the output signal intensity of the monitor light and the light intensity of the main light beam are proposed. According to the apparatus and the method, the output signal intensity of the monitor light detection unit and the light intensity of the main light beam on the target surface have a constant correlation regardless of the polarization state of the light incident on the light splitting element. Since the output of the monitor light beam detecting means is corrected, the light intensity of the main light beam on the image plane can be maintained at a predetermined level by the APC operation.

In the above-described light intensity control device and control method, the influence of the polarization state on the light incident on the light splitting element can be eliminated, but the polarization dependence of the light splitting element (the polarization component ratio of reflected light or transmitted light) is further improved. Has a problem that it changes due to a change in humidity (has a humidity-dependent characteristic). For example, since the coating surface of a half mirror formed of a dielectric coating is exposed to the outside air, the polarization component ratio of monitor light transmitted through the half mirror is likely to change due to changes in ambient humidity. Then, even with a light intensity control device provided with a means for correcting the polarization state of the incident light, the above-described APC operation cannot be executed accurately. Therefore, in this type of light intensity control device, it is necessary to perform control including the effect of a change in humidity.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and divides a main light beam and a monitor light beam by a light splitting element, and controls the light intensity of the main light beam on a target surface using the monitor light beam. Light intensity control device and light intensity control method capable of accurately controlling the light amount of a main light beam regardless of a change in polarization-dependent characteristics of a light splitting element depending on humidity The purpose is to obtain.

[0007]

SUMMARY OF THE INVENTION The present invention provides a light splitting element for splitting a light beam emitted from a light source unit having at least one light source into a monitor light beam and a main light beam, and monitor light detecting means for detecting the light intensity of the monitor light beam. Irrespective of the polarization state of the light incident on the light splitting element, the monitor light detecting means is configured such that the output signal intensity of the monitor light detecting means and the light intensity of the main light beam on the target surface have a constant correlation. A light intensity control device comprising: a polarization correction unit that corrects an output; and a control unit that controls light emission intensity of the light source unit based on an output signal of the monitor light detection unit corrected by the polarization correction unit. A reference light supply means provided independently of the light source unit, wherein a constant reference light is incident on the light splitting element in the same direction and at the same angle of incidence as the light beam emitted from the light source unit. The reference light detecting means for detecting the light intensity of the light beam in the same direction as the monitor light beam among the reference light beams incident on the light splitting device and the polarization dependent characteristics of the light splitting device depending on humidity are changed. When, the polarization-dependent characteristic change detecting means for detecting the amount of change in the polarization-dependent characteristic of the light splitting element from the change in the output signal of the reference light detecting means, the detected amount of change in the polarization-dependent characteristic of the light splitting element, Feedback means for feeding back to the polarization correction means, wherein the polarization correction means is based on the amount of change in the polarization-dependent characteristic of the light splitting element input from the feedback means, and the monitor light detection means irrespective of a change in humidity. The output of the monitor light detecting means is corrected so that the output signal intensity of the main light beam and the light intensity of the main light beam on the target surface have a constant correlation. The monitor light detecting means and the reference light detecting means may be light receiving elements provided independently of each other, or may be the same light receiving element.

According to the present invention, a light beam emitted from at least one light source is split into a monitor light beam and a main light beam by a light splitting element, and the monitor light beam emitted from the light source is detected by monitor light detecting means. The output signal of the monitor light detection means is polarized so that the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface have a constant correlation irrespective of the polarization state of the light incident on the element. In the light intensity control method of correcting the light emission intensity of the light source based on the output signal, the polarization characteristics are constant in the same direction and the same incident angle as the light flux of the light source unit incident on the light splitting element. Making the reference light incident on the light splitting element, and detecting the light intensity of the light flux in the same direction as the monitor light flux among the reference lights split into the light splitting element. Specifying the amount of change in the polarization dependent characteristic of the light splitting element depending on the humidity based on the output change of the transmitted reference light; feeding back the amount of change in the polarization dependent characteristic to the polarization correction means; The means has a constant correlation between the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface regardless of the humidity change, based on the input change amount of the polarization dependent characteristic of the light splitting element. Correcting the output of the monitor light detecting means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention will be described with reference to FIG. A beam scanning device having a light intensity control device schematically shown in FIG. 1 is a multi-beam light source 1 having a plurality of semiconductor laser oscillators and a plurality of optical fibers corresponding thereto.
0 is provided. The plurality of optical fibers have their emission sections fixed in a straight line, and the plurality of light beams emitted from the optical fibers reach the half mirror 11, which is a light splitting element, in a substantially parallel state. One part is transmitted through the half mirror 11 and the other part is the half mirror 1
1 is reflected by the coated surface. The light beam transmitted through the half mirror 11 is used as a monitor light beam as a beam splitter 12.
to go into. The beam splitter 12 converts each monitor beam into
The vibration direction of the electric field vector is separated into polarization components orthogonal to each other, and the two polarization components orthogonal to each other are detected by the light amount detection sensors 13 and 14, respectively. In the embodiment of FIG. 1, the monitor light beam is separated into P-polarized light and S-polarized light by the beam splitter 12, and the former is detected by the light amount detection sensor 13 and the latter is detected by the light amount detection sensor 14. On the other hand, the main light beam reflected by the half mirror 11 is reflected by the reflecting surface of the rotatable scanning polygon mirror 15, and the fθ lens provided between the polygon mirror 15 and the target surface (image surface 17). The light is imaged on the image plane 17 through 16.

The main light beam is scanned over the image plane 17 within a certain range by the rotation of the polygon mirror 15, and a light source power control circuit 18 is provided so that a predetermined light intensity is given to the image plane 17 according to the scanning position. Power control (including ON / OFF control) of the semiconductor laser oscillator is performed. Reference numeral 19 in FIG.
Is a reference voltage generation circuit for generating a reference voltage corresponding to a predetermined reference output of the laser.

The output signals of the two polarization components detected by the light quantity detection sensors 13 and 14 are respectively amplified by a first amplifier 20 and a second amplifier 21 and recombined by an addition circuit 22. The output recombined by the adding circuit 22 is amplified by the amplifier 23 and output as an APC signal. The reflection and transmission characteristics of the half mirror 11 have polarization-dependent characteristics. Even if the light source generates a laser beam of the same light intensity, the light amount detection sensor 13 and the light amount detection sensor 13 depend on the polarization state of the light beam incident on the half mirror 11. The ratio of each polarization component detected by the sensor 14 changes. Therefore, the output of the two polarization components of the monitor light beam is obtained by a half mirror 11 obtained from a design value or a measured value.
Amplification at a predetermined addition ratio (amplification rate) reflecting the polarization dependent characteristic of the light from the light amount detection sensors 13 and 14 depending on the change in the polarization state of the light beam incident on the half mirror 11 is corrected. be able to. Further, an optical element (the polygon mirror 1) from the half mirror 11 to the image plane 17 is provided.
Lens 5) and the fθ lens 16) also have less polarization than the half mirror 11, but also have polarization dependence. Therefore, if the above-mentioned addition ratio is set including the polarization dependence of the optical element downstream of the half mirror 11, Higher accuracy correction can be performed.

The APC signal generated through the above correction is input to the light source power control circuit 18. The light source power control circuit 18 sequentially outputs the APC signals of the respective semiconductor lasers to the reference voltage generation circuit 1 at a timing described later.
Then, the driving current of the light source is controlled so that the intensity of the beam spot on the image plane 17 becomes the intensity level set by the reference voltage. Then, in a section to be described later, the light source power control circuit 18 independently holds the APC signals of the respective semiconductor lasers generated through the correction so as to hold the intensity level of each beam spot at the reference level.

As described above, the monitor light beam is separated into polarization components orthogonal to each other, and each is calculated by a required addition ratio and then recombined, so that the monitor light beam is independent of the polarization state of each light beam incident on the half mirror 11. The sensor output of the monitor light can be adjusted so that the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface have a certain correlation. Thus, an accurate APC operation can be performed. That is, the frame A in FIG. 1 constitutes a circuit system for correcting the influence of the polarization dependence of the split optical system (and the scanning optical system) on the output of the monitor light beam. The correction circuit system A relating to the polarization dependency and the correction method thereof are described in detail in the above-mentioned Japanese Patent Application No. 8-75182 and the embodiments described later, and thus a specific description thereof will be omitted here.

The polarization dependence of the half mirror 11 is affected by changes in the humidity environment. Therefore, in the beam scanning device, a reference light source 24 is provided separately from the multi-beam light source 10. The reference light source 24 is the same as the light beam from the multi-beam light source 10 in the same direction and the same incident angle as the half mirror 11.
It is installed so that reference light may be incident on the. The reference light generated by the reference light source 24 has a property that the polarization characteristics are not changed by an environmental change. Further, an optical path is secured from the reference light source 24 to the half mirror 11 without using an optical fiber or the like whose polarization state changes easily depending on the layout and installation conditions so that the polarization state of the reference light does not change.

The reference light is split into reflected light and transmitted light by the half mirror 11, similarly to the light beam from the multi-beam light source 10. Among them, the reflection reference light (not shown) is blocked near the half mirror 11 so as not to affect the scanning by the polygon mirror 15. On the other hand, the amount of transmitted reference light is detected using a reference light detection sensor 25 provided behind the half mirror 11. An output signal of the light amount of the transmitted reference light detected by the reference light detection sensor 25 is output from an amplifier 26.
After that, it is input to a feedback circuit 27 connected to the correction circuit system A. Since the reference light is not changed in the polarization characteristic until it enters the half mirror 11, the change in the amount of transmitted reference light detected by the reference light detection sensor 25 depends on the polarization of the half mirror 11. It is detected as a change in characteristics. As described above, the change in the polarization-dependent characteristics of the half mirror 11 depends on the change in the humidity environment.
7 means that the influence of the humidity change is detected.

The feedback circuit 27 feeds back the amount of change in the polarization dependent characteristic of the half mirror 11 to the correction circuit system A. In response to this, the correction circuit system A calculates the above-mentioned addition ratio for the two orthogonal polarization components (P-polarized light and S-polarized light) of the monitor light beam based on the input change amount of the polarization dependence characteristic of the half mirror 11. Reset it,
An APC signal is generated by controlling the output signal intensity of the monitor light beam and the light intensity of the main light beam on the image plane 17 so as to maintain a constant balance regardless of the change in humidity. In the example of FIG. 1, the adjustment of the amplification factor for the correction of the humidity dependency is performed on the output of the polarization component (S-polarized light) detected by the light amount detection sensor 14.

That is, the frame B in FIG. 1 constitutes a correction circuit system for correcting the influence of the humidity dependence of the half mirror 11. By linking the correction circuit system B for humidity dependency with the correction circuit system A for polarization dependency described above, in addition to the change of the polarization state of the light beam incident on the half mirror 11, the polarization dependency of the half mirror 11 due to the change in humidity is obtained. Even when the characteristics change, the outputs of the light amount detection sensors 13 and 14 are corrected so that the light intensity of the main light beam on the image plane 17 and the output signal intensity of the monitor light detection means have a constant correlation. . Therefore, it is possible to control the light amount of the main light beam with high accuracy.
In FIG. 1, the reference light detection sensor 25 is provided separately from the light amount detection sensors 13 and 14 for monitor light detection. However, it is also possible to detect the transmitted reference light using the light amount detection sensors 13 and 14. is there.

Next, a specific embodiment of the light intensity control device and its control method will be described with reference to FIGS.
This light intensity control device 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, a schematic configuration of the scanning optical device will be described with reference to FIGS. In the following description, “main scanning direction” is a direction corresponding to the scanning direction of the light beam in a plane perpendicular to the optical axis, and “sub-scanning direction” is a direction perpendicular to the main scanning direction in a plane perpendicular to the optical axis. Shall be referred to.

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. 2 and 5, the light source unit 100 of the scanning optical system includes eight laser blocks 310a to 310h mounted on a support substrate 300, respectively.
And 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 the drawing) for emitting a light beam emitted from the semiconductor laser to the optical fiber. ), And a fiber alignment block 130 which forms eight point light sources arranged in a straight line by holding the ends of the optical fibers on the emission side in a straight line. In addition,
The incident-side ends of the optical fibers 121 to 128 are held by fiber supports 319a to 319h fixed to the laser blocks 310a to 310h.

The 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 P-polarized light oscillating in the incident surface of the light splitting surface of the half mirror and the S-polarized light oscillating in the surface perpendicular to the incident surface.
It is.

The monitor light beam transmitted through the half mirror 144 is incident on an APC signal detecting section 150 which constitutes a light detecting means and a correcting means of the light intensity control device. The APC signal detection unit 150 is a condenser lens 1 that converges a transmitted light beam.
51, a polarization beam splitter 153 as a polarization separation element that separates this light beam into two orthogonal polarization components,
It comprises an APC first light receiving element 155 and an APC second light receiving element 157 for detecting the light energy of each polarized light component, and the output signal is a semiconductor laser 10
It is used to feedback-control the outputs 1 to 108.

On the optical path of the main light beam reflected by the half mirror 144, a cylindrical lens 170 is provided. The cylindrical lens 170 is held by a cylindrical cylindrical lens holder 361,
As shown in FIGS. 3 and 5, two lenses 171 and 1 having positive and negative powers in the sub-scanning direction, respectively.
73.

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 cut off from the outside air by a cup-shaped polygon cover 373 as shown in FIG. 2 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.

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. 4, the light is reflected by the folding mirror 200, reaches the photosensitive drum 210, and forms 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 driven to rotate 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.

The light beam 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 fθ lens 190 and the return mirror 200, and reflects a light beam in front of the drawing range, and is reflected by the first mirror 221. Second and third mirrors 22 for sequentially reflecting light beams
3, 225 and a light receiving element 230 for receiving 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 are sequentially incident on the light receiving element 230 one by one in accordance with the scanning, and the light receiving element 230 outputs eight pulses for each scanning. 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.

Further, near the half mirror 144, a reference light source 111 constituting the humidity dependency correction unit 110 (FIGS. 11 and 12) is provided. The reference light source 111 generates reference light separately from the semiconductor lasers 101 to 108,
This reference light is transmitted to the fiber alignment block 13
The light is emitted toward the half mirror 144 from the same direction as 0.
The reference light source 111 always generates reference light with constant polarization characteristics, and an optical path between the reference light source 111 and the half mirror 144 without using an optical member that may change the polarization characteristics of the reference light, such as an optical fiber. Is secured. In other words, the reference light is incident on the half mirror 144 in the same direction and at the same incident angle as the eight laser light beams collimated by the collimating lens 140 with a constant polarization characteristic. Then, the reference light is split into the reflection reference light and the transmission reference light by the half mirror 144. Among them, the reflection reference light (not shown) may be harmful to scanning using the main light beam, and is shielded by a light shielding member (not shown). On the other hand, the light intensity of the transmitted reference light traveling in the same direction as the monitor light beam is detected by the reference light detection light receiving element 112. The output signal related to the transmitted reference light is taken in the process of generating the APC signal and used for feedback control of the laser output. This control process will be described later.

Next, the details of each component of the above-described scanning optical system will be described with reference to FIGS. FIG.
Is a cross-sectional view showing a specific configuration of the laser block 310a, and FIG. 7 is a front view of FIG. 6 as viewed from the direction of the line VII-VII. In addition, the laser blocks 310a to 310h
All have the same structure, and therefore 310a will be described as a representative. As shown in these figures, the laser block 310a includes a semiconductor laser holding member 311a for holding the semiconductor laser 101 and a coupling lens holding member 31 for holding the coupling lens 111.
3a and a fiber fixing member 315a to which the fiber support 319a is fixed.

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. 6, the incident end face of the optical fiber 121 is set to be inclined so as not to be orthogonal to the incident optical axis. Further, the fiber support 319a is also arranged so as to be inclined as a whole so 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 spreads,
A predetermined spot diameter cannot be obtained on the image plane, and the drawing accuracy deteriorates. By preventing return light, such a problem can be avoided.

The exit ends of the optical fibers 121 to 128 are combined by a fiber alignment block 130 as shown in FIG. 8, and at the exit end, the center axes of the optical fibers are aligned in a straight line in FIG. Is positioned as

Fiber alignment block 130
Is held by a holder (not shown), and the photosensitive drum 210
The straight line connecting the central axes of the fibers is set obliquely so as to form a predetermined angle with respect to the main scanning direction so that the above beam spots are formed at predetermined intervals in both the main scanning direction and the sub-scanning direction.

FIG. 10 shows an arrangement of beam spots on the photosensitive drum. By arranging the end faces of the plurality of optical fibers serving as object points on a straight line oblique to the main scanning direction, the beam spot is also formed such that the centers of the beam spots are aligned. 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, an APC signal detecting section 150 constituting a main part of the light intensity control device included in the above-described scanning optical device.
The operation of the humidity dependency correction unit 110 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 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 light beams emitted from the respective optical fibers are The polarization states are different from each other. In addition, the polarization state also changes due to a change in the attitude of the fiber or a change in the environment. When an actual device is assembled, a change in the condition that changes the polarization state can easily occur.

On the other hand, most optical elements constituting the scanning optical system have polarization-dependent characteristics in reflectance or transmittance, and in particular, the half mirror 144 has large polarization-dependent characteristics. For example, when 7.5% of the total light amount is used as the monitor light flux, the transmittance of the half mirror is about 10% for P-polarized light and about 5% for S-polarized light in typical coating characteristics.

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. That is, although the APC originally controls the light amounts of the beam spots on the surface of the photosensitive drum to be equal, the difference in the light amount is rather increased by performing the control in the conventional method.

Since the light quantity of the beam spot is related to the density of the pattern to be printed, if there is a relative difference in the light quantity among a plurality of beams, a desired density balance cannot be obtained.
For example, there is a problem that the density becomes non-uniform in a portion where a uniform density is desired. Such a disadvantage can be avoided by eliminating the polarization dependent characteristic 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, in view of the thin film forming technology,
In practice, it is difficult to create a surface having a small polarization dependence. If the difference between the reflectance and the transmittance is reduced, a half mirror having a small polarization-dependent characteristic can be created, but in this case, the efficiency of use as a main light beam used for drawing is reduced, and the output of the light source is reduced. When the light source 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 the light by the second APC light receiving element 157, the output signals Ss and Sp of each light receiving element are expressed by the following equation [1].
The APC signal S is obtained by applying a predetermined weight to the APC signal, and the output of each semiconductor laser is feedback-controlled based on the signal S, thereby solving the above-mentioned problem relating to the polarization dependence. [1] 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 [2], and is calculated from optical design data once the optical system of the device 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. [2] k = k1 × k2 where k1 = Mp / Ms and k2 = Ps / Pp.
Mp and Ms are the light intensities of the transmitted light (monitor light flux) when two linearly polarized light beams whose vibration directions of the electric field vector are orthogonal to each other are incident on the half mirror 144, and Ps and Pp are the values at that time. Is the light intensity of the reflected light (main light flux) on the image plane. Typically, these can be measured 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.

Assuming that the splitting characteristics of the polarization beam splitter 153 are perfect, the component incident on the half mirror 144 as P-polarized light is the first light receiving element 155.
And the component incident as S-polarized light
It is detected only by the 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 set to 5%, and the transmittance Hp of P-polarized light is set to 10%.
The optical element on the 0 side, that is, the cylindrical lens 17
0, the polygon mirror 180, the fθ lens 190, and the polarization mirror 200 are combined, and the loss due to these elements is assumed to be 10% for P-polarized light and 1% for S-polarized light. Thereby, the half mirror 14
The ratio Dp of the amount of light reaching the photosensitive drum 210 out of the P-polarized light reflected at 4 is 90%, and similarly, the ratio Ds of the amount of light of the S-polarized light is 99%. In this case, the above coefficients k1 and k2
Is as follows. k1 = Mp / Ms = Hp / Hs = 2 k2 = Ps / Pp = {(l-Hs) .Ds} / {(1Hp) .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, the intensities Sp and Ss of the respective polarization components of the monitor light flux are calculated by the above equation S = K (Sp + k · Ss).
Are respectively shown by substituting into APC control amounts. Here, APC is performed so that the intensity of the other P-polarized light and the circularly-polarized light is made to match the intensity of the S-polarized light with reference to the intensity of the S-polarized light.
An example of control is shown. 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.

[0047]

Table 1 Monitor APC Light intensity on drum 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 0.0050 0.941 0.941 0.941 circularly-polarized light 075 0.075 0.874 0.583

[0048]

[Table 2] Monitor light flux intensity APC Light intensity on drum Sp Ss Control amount (S) No APC APC activated P-polarized 0.100 0.000 0.0050 0.810 0.940 S-polarized 0.000 0.050. 058 0.941 0.941 Circularly polarized light 0.050 0.025 0.054 0.874 0.939

In the example shown in Table 1, P-polarized light and S-
When polarized light is incident, the APC is operated to allow a maximum of about 2.3 (= 0.941 /) on the photosensitive drum surface.
0.4405) times the intensity difference occurs, and the density of the latent image formed on the photosensitive 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.

In the above example, both the polarization dependence of the half mirror 144 and the polarization dependence of the optical element on the photosensitive drum 210 side are taken into consideration.
Although the control is performed so as to suppress the change in the amount of light on the surface 10, it is also possible to perform the control in consideration of only the polarization dependence characteristic of the half mirror 144 having the most remarkable polarization dependence. In this case, the APC signal S is obtained by the following equation [3].
The symbols in the formula are the same as those in the above formula. [3] S = K (Sp + k1 · Ss) As described above, when 5 to 10% of the total light amount is divided and used as the monitor light, the intensity ratio of the monitor light is, for example, S-polarized (5%) depending on the polarization direction. ) And P-polarized light (10%) are about twice as large, while the intensity ratio of the main luminous flux after splitting the monitor light is S-polarized light (95%) and P-polarized light (90%) in the above example. Is about 1.06 times, and the ratio of the intensity change depending on the polarization is small as compared with the monitor light having a low light intensity ratio. Therefore, it is effective to correct only the polarization dependence of the transmittance of the half mirror 144.

Table 3 below shows data similar to 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.

[0052]

Table 3 Monitor light flux intensity APC Light intensity on drum Sp Ss Control amount (S) No APC APC activated P-polarized 0.100 0.000 0.0050 0.810 0.810 S-polarized 0.000 0.050. 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.

As described above, the monitor light beam is separated into polarized light components in a plurality of directions, and the laser power is controlled in consideration of the difference in the polarization state of each beam detected from the ratio of the polarized light components. It is possible to control so that the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface always have a constant correlation irrespective of the polarization state of the light incident on the mirror. Becomes possible.

However, as described above, the half mirror 14
The polarization dependent characteristic of No. 4 has humidity dependency. For example,
When the monitor light beam is separated into P-polarized light and S-polarized light as described above, even if the polarization state and the amount of incident light are constant,
The light intensity detected by the first light receiving element 155 and the second light receiving element 157 changes due to a change in humidity. Therefore, under the condition where the humidity changes, it is not possible to cope with the correction method in which the polarization dependent characteristic of the half mirror 144 is set to a fixed value.

For example, as described above, for P-polarized light, 1
When the half mirror 144 having a transmittance of about 5% for the S-polarized light is used as the set value, the half mirror 144 receives 12% for the P-polarized light due to the humidity change.
It is assumed that the transmittance of S-polarized light has changed to about 3% (7.5% of the total light amount is transmitted as a monitor light flux). In this case, the above equation [1] is used by using the above coefficient k.
Table 4 below shows the APC control amounts obtained for the P-polarized light, S-polarized light, and circularly polarized light having the same power, and the results of the adjustment of the light intensity on the image plane, based on the above method. Show. However, conditions other than the polarization dependence characteristics of the half mirror are the same as those in Table 2.

[0057]

Table 4 Monitor light flux intensity APC Light intensity on drum Sp Ss Control amount (S) No APC APC operation P-polarized 0.120 0.000 0.0060 0.792 0.462 S-polarized 0.000 0.0030 0.0 035 0.960 0.960 Circularly polarized light 0.060 0.015 0.047 0.876 0.653

As described above, when the APC is operated based on the initial optical setting value with the polarization dependent characteristic of the half mirror 144 changed, when the P-polarized light and the S-polarized light enter, the photosensitive drum surface In this case, a light intensity difference of up to twice or more is generated, which is not practical. This is because the transmittance (Hp, Hp) of each polarization component of the half mirror 144 is
s) and the ratio (Dp, Ds) of each polarized light component reaching the photosensitive drum 210, that is, the coefficient k, is kept at the above set value without taking into account the change in the polarization dependent characteristic of the half mirror 144 due to humidity. This is because the operation is performed.

In order to solve this problem, the apparatus according to the embodiment is provided with a humidity dependency correction unit 110 to detect the change in the polarization dependency of the half mirror 144 due to the humidity change.
This is fed back to the generation of the signal S.

As described above, reference light having a constant polarization characteristic is incident on the half mirror 144 from the reference light source 111.
Part of the light passes through the half mirror 144 and the light intensity is detected by the reference light detecting light receiving element 112. Since the reference light has a constant polarization characteristic, by monitoring the change in the light intensity detected by the reference light detecting light receiving element 112, it is possible to know the change in the polarization dependent characteristic of the half mirror 144 due to humidity. In this embodiment, the half mirror 14 has a transmittance of 10% for P-polarized light and a transmittance of 5% for S-polarized light.
4 is the initial set value, and the light-receiving element 1
By monitoring the output signal of the half mirror 144, the change amount (P
Change in the transmittance of polarized light and S-polarized light). Then, the amount of change in the polarization dependent characteristic is fed back to the circuit for obtaining the APC signal S. The above equation [1]
In other words, the value of the coefficient k may be reset based on the new polarization dependence characteristic of the specified half mirror 144, and the APC signal (S) may be calculated based on the value. As in the present embodiment, the transmittance Hs of S-polarized light changes from 5% to 3%,
Assuming that the transmittance Hp of the P-polarized light has changed from 10% to 12%, the amount of change can be detected through the light intensity of the transmitted reference light detected by the light receiving element 112 for reference light detection. Are substituted into the above equation [2] as the proper transmittances Hs and Hp. The ratio Dp of the amount of P-polarized light reaching the photosensitive drum 210 and the ratio Ds of the amount of S-polarized light Ds
Can be obtained from the changes in the transmittances Hs and Hp of the half mirror 144 and the loss rate (set value) of each polarization component by the optical element on the photosensitive drum 210 side from the half mirror 144. Therefore, by monitoring the transmitted light of the reference light incident on the half mirror 144, a new coefficient k is obtained.
In this case, the value of the coefficient k is k ≒ 4.
85. In Table 5 below, under the same conditions as in Table 4, the coefficient k reflecting the change in the polarization dependent characteristic of the half mirror 144 is shown.
Shows the APC control amount obtained by using the above equation [1] and the result of adjusting the light intensity on the image plane.

[0061]

[Table 5] Monitor light flux intensity APC Drum light intensity Sp Ss Control amount (S) No APC APC operation P-polarized 0.120 0.000 0.0060 0.792 0.964 S-polarized 0.000 0.0030 0.0 073 0.960 0.960 Circularly polarized light 0.060 0.015 0.067 0.876 0.955

As described above, the means for detecting the amount of change in the polarization dependent characteristic of the half mirror 144 is provided, and the light receiving elements 155 and 1 depending on the polarization dependent characteristic of the half mirror 144 are provided.
By resetting the addition ratio of the outputs of 57 in accordance with the amount of change in the polarization dependent characteristic, the beam power on the drum surface when APC is applied can be corrected to the same level as the results in Table 2 above. Become. Note that, in Tables 4 and 5, an example in which the APC signal (S) is obtained using Expression [1] has been described. However, even in a method in which only the polarization dependence of the half mirror 144 is taken into consideration as in Expression [3], the humidity may be reduced. An effective AP is obtained by feeding back the amount of change (transmittance Hp, Hs) of the polarization dependence characteristic of the half mirror 144 obtained by the dependence correction unit 110.
C operation can be performed.

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 that is dot data for each pixel and outputs the converted signal; laser driving circuits 451 to 458 that drive the semiconductor lasers 101 to 108 on / off based on the drawing signals; , An APC signal generation circuit 430 that generates an APC signal based on the outputs of the second light receiving elements 155 and 157, and 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.

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 individually emit light sequentially in order to obtain an APC signal, and is output to each of the laser drive 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 further outputs the polarization dependence of the half mirror 144 from the humidity dependence correction unit 110. Data representing the amount of change in characteristics is taken in, and an APC signal of each semiconductor laser is output based on the data. 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, the switch SW1 is turned on for a certain period of time during which the first semiconductor laser 101 emits light, 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 drive 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 luminous flux from 108 differs 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 generation 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. 12, the APC signal generation circuit 430 receives the P-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 APC signal. 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 at the time of adjusting the assembling amount. As described above, the APC signal S relating to the S-polarized light component outputs the output voltages of the light receiving elements 155 and 157 as Sp,
When Ss is appropriately amplified (K times), it can be obtained by the above equation [1].

FIGS. 11 and 12 further show a humidity dependency correction unit 110. FIG. Humidity dependency correction unit 110
Is a reference light amplifier 11 for amplifying an output signal of the reference light detection light receiving element 112 for detecting the light intensity of the transmitted reference light.
3 and a feedback circuit 114 for specifying the amount of change in the polarization dependency of the half mirror 144 based on the output of the reference light amplifier 113 and feeding back the amount of change to the gain adjustment circuit 433. The gain adjustment circuit 433 resets the addition ratio (coefficient k) of the P-polarized component and the S-polarized component according to the input change amount of the polarization dependent characteristic. As described above, by linking the humidity dependency correction unit 110 with the APC signal generation circuit 430, in addition to the change in the polarization state of the light beam incident on the half mirror 144, the change in the polarization dependency of the half mirror 11 due to the humidity change. The output of the light receiving elements 155 and 157 is corrected so that the light intensity of the main light beam on the photosensitive drum 210 and the output signal intensity of the monitor light detecting means have a constant correlation even with the change, and the APC is operated accurately. Can be done.

The structure of the laser drive circuit 451 is shown in FIG.
It is as shown in FIG. The sample hold circuit 451a
When a timing signal is input from the timing signal generation circuit 410, the APC is synchronized with the turning on of the switch SW1.
The APC signal output from the signal generation circuit 430 is captured and held. On the other hand, reference voltage generation circuit 451b
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 driving current at this time can be adjusted by the gain set by the differential amplifier. . With the above configuration, the laser drive circuit 451c 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. 14 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 states of the semiconductor lasers 101 to 108, the ON / OFF states of the switches SW1 to SW8 of the switching circuit 440, and the output timing of the horizontal synchronizing signal HS are shown on the horizontal axis. It is displayed on the 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 synchronization 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 t2, and the semiconductor laser 102 emits light between t2 and t3, and the switches SW1 and SW2 are turned on during these periods. 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 to detect the eight horizontal lines for each scanning line. 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 lapse of a predetermined time 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. It is formed by controlling 103 and 108. Since the beam spots formed by the luminous flux from each semiconductor laser are separated by a predetermined amount in the main scanning direction,
By starting writing by the next beam spot at the time when scanning is performed by a predetermined amount after writing by the preceding beam spot is started, the positions of the scanning lines on the photosensitive drum 210 in the main scanning direction can be aligned. .

In the above embodiment, the first light receiving element 155 for APC and the second light receiving element 157 for APC used as a monitor of the scanning light intensity, and the light receiving element 112 for the reference light detection for detecting the light intensity of the reference light. However, if the light emission timing and the like of the light source unit 100 and the reference light source 111 of the scanning optical system are controlled, the reference light can be detected by the light receiving element for monitoring the scanning light amount.

In the above, when correcting the polarization state of the light beam incident on the half mirror 144, the output signal intensity (A
Due to the adjustment based on the PC signal S), a method of resetting only the coefficient k relating to the output signal intensity of the S-polarized light in accordance with a change in humidity is adopted. It is not limited.

For example, the output signal intensity of the P-polarized light of the separated monitor light beam may be changed according to the change in humidity. In this case, the humidity dependency correction unit is configured as shown in FIG. FIG. 2 shows a scanning optical device having substantially the same configuration as the scanning optical device 10 of FIG. 1, and the same members or circuits as those of FIG. 1 are denoted by the same reference numerals. The monitor light beam is separated into a P-polarized light component and an S-polarized light component that are orthogonal to each other by a beam splitter 12, and the light amount of the former is detected by a light amount detection sensor 13, and the latter is detected by a light amount detection sensor 14. In the correction circuit system B1 relating to the humidity dependency, the light intensity of the reference light detected by the reference light detection sensor 25 and electrically amplified by the amplifier 26 is input to the feedback circuit 40. The feedback circuit 40 is a light amount detection sensor 1 for P-polarized light in the correction circuit system A1 for polarization dependence.
3 is connected to the first amplifier 20 for adjusting the output. In this embodiment, the amount of change in the polarization-dependent characteristic of the half mirror 11 due to a change in humidity is detected using the reference light, and the output signal intensity of the APC signal recombined by the adder circuit 22 in accordance with the amount of change. In the first amplifier 20, the output signal intensity of the P-polarized light of the monitor light is adjusted so that the light intensity of the main light beam on the image plane 17 has a certain correlation.

FIG. 16 also shows a different form, and the same members or circuits as those in FIG. 1 are denoted by the same reference numerals. The humidity dependency correction unit B2 in the scanning optical device shown in FIG. 3 includes two amplifiers 5 that electrically amplify the output of the reference light detection sensor 25.
1 and 52, and the outputs of the amplifiers 51 and 52 are input to feedback circuits 53 and 54. The feedback circuit 53 is configured to control the S
The feedback circuit 54 is connected to the first amplifier 20 for P-polarization, and is connected to the second amplifier 21 for polarization. In this embodiment, the amount of change in the polarization-dependent characteristic of the half mirror 11 due to a change in humidity is detected using the reference light, and the output signal intensities of the P-polarized light and the S-polarized light of the monitor light are detected in accordance with the amount of change. The adjustment at the same time can correct the humidity dependency.

FIG. 17 shows still another embodiment. In this figure, the same members or circuits as those in FIG. 1 are indicated by the same reference numerals. Humidity-dependent correction unit B in this scanning optical device
The beam splitter 3 includes a beam splitter 60 that separates the reference light into P-polarized light and S-polarized light, similarly to the beam splitter 12.
The P-polarized light intensity of the reference transmitted light is equal to the first light for the reference light detection.
The output signal strength detected by the sensor 61 is
And input to the feedback circuit 65.
Similarly, the light intensity of the S-polarized light is determined by the second sensor 6 for reference light detection.
2, the output signal strength is amplified by the amplifier 64 and input to the feedback circuit 66. In this embodiment, with respect to the polarization-dependent characteristics of the half mirror 11, it is possible to individually detect changes in the polarization components (P-polarized light and S-polarized light) of the reference transmitted light separated by the beam splitter 60. Therefore, the amount of change of each polarization component in the reference transmitted light is
The first amplifier 20 for P-polarized light and the second amplifier 21 for S-polarized light in the correction circuit system A3 for polarization dependency
And the output signal intensities of the P-polarized light and the S-polarized light of the monitor light can be individually adjusted to correct the humidity dependency.

As is apparent from the above description, the reference light detecting means, the means for detecting a change in the polarization dependent characteristic, and the feedback means are not limited to those shown in FIGS. In short, it is only necessary that the APC signal obtained by recombining the output signal intensities of the separated polarized light components with respect to the monitor light beam is adjusted to reflect the humidity change.

The light intensity control device of the present invention is particularly effective when used in the above-described scanning optical device. However, the application is not limited to the scanning optical device, but can be applied to other optical devices. Is also good.

[0085]

As described above, according to the present invention,
Since the amount of change in the polarization-dependent characteristic of the light splitting element that splits the monitor light beam and the main light beam using the reference light having a constant polarization state is specified, and this change amount is fed back to generate the APC signal, the light splitting element is used. Irrespective of changes in the humidity environment around the light source, it is possible to accurately control the amount of the main light beam. Therefore, for example, if the light intensity control device and the control method of the present invention are used in a multi-beam scanning optical system including a plurality of light sources, the light beam incident on the light splitting element has polarization state and humidity dependency. Even if the polarization dependence of the reflection / transmission characteristics of the light splitting element changes, the intensity of the spot on the scanning target surface can be accurately controlled based on the monitor light beam without depending on these changes.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an optical scanning device having a light intensity control device.

FIG. 2 is a perspective view showing a specific embodiment of a scanning optical device having a light intensity control device.

FIG. 3 is a plan view of the apparatus of FIG. 2 in the main scanning direction.

FIG. 4 is a sectional view in the sub-scanning direction of the apparatus of FIG. 2;

FIG. 5 is an explanatory view in the main scanning direction showing only the optical system of the apparatus shown in FIG. 2;

FIG. 6 is a sectional view showing details of a laser block portion of the apparatus shown in FIG. 2;

FIG. 7 is a front view of FIG. 6 as viewed from the direction of line VII-VII.

FIG. 8 is a plan view showing a configuration from a fiber support to a fiber alignment block of the apparatus of FIG. 5;

FIG. 9 is an enlarged front view of the fiber alignment block.

FIG. 10 is an explanatory diagram showing an arrangement of beam spots on a photosensitive drum.

FIG. 11 is a block diagram illustrating a control system of the scanning optical device according to the embodiment.

FIG. 12 is a block diagram showing details of an APC signal generation circuit and a humidity dependency correction circuit in FIG. 11;

FIG. 13 is a block diagram showing details of a laser drive circuit in FIG. 11;

FIG. 14 is a timing chart illustrating the operation of the scanning optical device according to the embodiment.

FIG. 15 is a schematic diagram illustrating a different embodiment of a scanning optical device having a light intensity control device.

FIG. 16 is a schematic diagram showing an embodiment different from FIG. 15 of the scanning optical device having the light intensity control device.

FIG. 17 is a schematic view illustrating still another embodiment of a scanning optical device having a light intensity control device.

[Explanation of symbols]

 Reference Signs List 10 multi-beam light source 11 half mirror 12 beam splitter 13 14 light quantity detection sensor 15 polygon mirror 16 fθ lens 18 light source power control circuit 19 reference voltage generation circuit 22 addition circuit 24 reference light source 25 reference light detection sensor 27 feedback circuit 100 light source units 101 to 101 Reference Signs List 108 semiconductor laser 110 humidity dependency correction unit 111 reference light source 112 reference light detection light receiving element 113 reference light amplifier 114 feedback circuit 121 to 128 optical fiber 130 fiber alignment block 140 collimating lens 144 half mirror 150 APC signal detection unit 153 polarization beam splitter 155 APC first light receiving element 157 APC second light receiving element 180 Polygon mirror 190 fθ lens 210 Photoconductor drum 43 APC signal generating circuit 433 gain adjustment circuit 451 to 458 laser drive circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 26/10 G11B 7/125

Claims (4)

(57) [Claims] A light splitting element for splitting a light beam emitted from a light source unit having at least one light source into a monitor light beam and a main light beam; monitor light detecting means for detecting the light intensity of the monitor light beam; The output of the monitor light detection means is corrected so that the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface have a fixed correlation regardless of the polarization state of the light incident on the element. A light intensity control device comprising: a polarization correction unit; and a control unit that controls the emission intensity of the light source unit based on the output signal of the monitor light detection unit corrected by the polarization correction unit. A reference light supply unit provided independently of the light source unit, for causing the reference light to enter the light splitting element in the same direction and at the same angle of incidence as the light beam emitted from the light source unit; Reference light detecting means for detecting the light intensity of the light beam in the same direction as the monitor light beam among the reference light beams incident on the element and splitting; when the polarization dependent characteristic of the light splitting element depending on humidity is changed Polarization-dependent characteristic change detecting means for detecting a change in the polarization-dependent characteristic of the light splitting element from a change in the output signal of the reference light detecting means; Feedback means for feeding back to the correction means, wherein the polarization correction means detects the monitor light detection means irrespective of humidity change based on the amount of change in the polarization dependent characteristic of the light splitting element input from the feedback means. A light intensity control device for correcting the output of the monitor light detecting means so that the output signal intensity and the light intensity of the main light beam on the target surface have a fixed correlation. 2. The light intensity control device according to claim 1, wherein said monitor light detecting means and said reference light detecting means comprise:
A light intensity detection device which is a light receiving element provided independently. 3. The light intensity control device according to claim 1, wherein the monitor light detection means and the reference light detection means
A light intensity detector that is also used by the same light receiving element. 4. A light beam emitted from at least one light source is split into a monitor light beam and a main light beam by a light splitting element, the monitor light beam emitted from the light source is detected by monitor light detecting means, and the light beam is transmitted to the light splitting element. Irrespective of the polarization state of the incident light, the output signal of the monitor light detection unit is polarized by the polarization correction unit so that the output signal intensity of the monitor light detection unit and the light intensity of the main light beam on the target surface have a constant correlation. Amend,
In the light intensity control method of controlling the light emission intensity of the light source based on the output signal, the reference light having the same polarization characteristic and the same direction as the light beam of the light source unit incident on the light splitting element is split. Making the light incident on the element; detecting the light intensity of the light beam in the same direction as the monitor light beam among the reference light beams incident on the light splitting element and splitting; Specifying the amount of change in the polarization dependent characteristic of the light splitting element depending on humidity; the step of feeding back the amount of change in the polarization dependent characteristic to the polarization correction means; Based on the amount of change in the polarization-dependent characteristics of the element, the above-mentioned monitor is set so that the output signal intensity of the monitor light detection means and the light intensity of the main light beam on the target surface have a constant correlation regardless of the humidity change. Correcting the output of the monitor light detecting means.