JPH05303049A - Optical scanner for reducing shading - Google Patents

Abstract

PURPOSE:To effectively reduce shading based on a polarized light of a laser luminous flux. CONSTITUTION:In the optical scanner for using a semiconductor laser or a semiconductor laser array as a light source 1, deflecting a laser luminous flux from the light source 1 by an optical deflecting means having the deflecting/ reflecting surface 5, condensing it as a light spot onto the surface 9 to be scanned, by a scanning lens 6 and executing an optical scan, reflection reducing coating 11 is provided only on the refracting surface on which an incident angle is varied most greatly in connection with a deflection of the laser luminous flux, in the optical element surface which is provided on an optical path for reaching on the surface 9 to be scanned from the optical deflecting means and allows the laser luminous flux to transmit through.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device with reduced shading.

[0002]

2. Description of the Related Art An optical scanning device that optically scans a surface to be scanned, which is set to match the surface of an optical recording medium such as a photoconductor, with a laser beam is widely known in connection with laser printers and the like. In a general optical arrangement of an optical scanning device, a laser light beam from a laser light source is deflected by an optical deflecting means such as a rotating polygon mirror and is made into a light spot on a surface to be scanned by a scanning lens. Therefore, the incident angle of the laser light flux on the deflective reflection surface of the light deflector and the scanning lens continuously changes during the optical scanning of one line. Since the reflectance on the deflecting / reflecting surface and the reflectance / transmittance on the lens surface of the scanning lens change depending on the incident angle, the light intensity of the light spot on the surface to be scanned generally changes with the image height.
The fluctuation of the light intensity in one line of the optical scanning is called "shading". Shading is remarkable when the light beam incident on the deflecting / reflecting surface is linearly polarized light. Generally, the light intensity is smaller on both end sides in the main scanning direction than the center image height, or conversely, the center image height is higher. On the other hand, there is a tendency that the light intensity increases on both end sides in the main scanning direction.

A laser beam emitted from a semiconductor laser or a semiconductor laser array used as a light source of an optical scanning device has an extinction ratio of about 20 dB, and most of the linearly polarized light component is apt to cause shading. In the near future,
In order to reduce the size of the optical scanning device, the angle of view of the optical scanning is widened, and the variation area of the incident angle also becomes large, so that the shading tends to increase. On the other hand, there is a demand for higher quality of the recorded image by optical scanning, and deterioration of the image quality of the recorded image due to shading is becoming a problem.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide an optical scanning device with reduced shading.

[0005]

An optical scanning device to which the present invention is provided is "a semiconductor laser or a semiconductor laser array is used as a light source, and a laser beam from the light source is deflected by an optical deflecting means having a deflecting reflecting surface. It is an optical scanning device for performing optical scanning by condensing a light spot on the surface to be scanned by the scanning lens.

In such an optical scanning device, an optical path extending from the light source to the surface to be scanned is assumed to be a virtual optical path linearly expanded along the optical axis, and at an arbitrary position on the virtual optical path, A direction corresponding to the main scanning direction in parallel is called a main scanning corresponding direction, and a direction corresponding to the sub scanning direction in parallel is called a sub scanning corresponding direction.

In order to reduce the shading, the optical scanning device according to the first aspect of the present invention includes: "A laser beam of the optical element surface which is provided on the optical path from the optical deflecting means to the surface to be scanned and transmits the laser beam. The antireflection coating is provided only on the refracting surface where the incident angle changes the most with the deflection.

In order to reduce shading, an optical scanning device according to a second aspect of the present invention has an "anti-reflection coating on one or more lens surfaces of a scanning lens, wherein the transmittance of the scanning lens is at both ends in the main scanning corresponding direction from the optical axis. It is provided so as to increase gradually toward the section. "

In order to make the transmitted light of the scanning lens gradually increase from the optical axis toward both ends in the main scanning direction, "an antireflection coating provided on one or more lens surfaces of the scanning lens is required. May be set to be "thicker than the optimum film thickness for the wavelength of the laser beam" (Claim 3), or "the film of the antireflection coating provided on one or more lens surfaces of the scanning lens". The thickness may be set so as to gradually increase from the lens optical axis portion toward both ends in the main scanning corresponding direction (claim 4).

The optical scanning device can also be one in which one or more mirrors for bending the optical path of the laser beam are provided between the optical deflecting means and the surface to be scanned.

In the optical scanning device according to the fifth aspect, the mirror for bending the optical path of the laser light beam is formed in this way.
In the optical scanning device having the above, "a reflection enhancing coating is provided on the mirror surface of one or more mirrors and the reflectance of the reflection enhancing coating is set to gradually increase from the central portion toward the both ends in the main scanning corresponding direction". Characterize. In order to carry out this concretely, "the film thickness of the reflection-increasing coat may be gradually increased from the central portion in the main scanning corresponding direction toward both ends" (claim 6), or "increased". The thickness of the reflective coat,
The thickness may be set to be thicker than the optimum film thickness for the wavelength of the laser beam ”(claim 7).

An optical scanning device according to an eighth aspect is the optical scanning device described above, wherein "1 is provided on an optical path between the light source and the optical deflecting means.
A quarter wave plate is provided so that the laser light flux incident on the light deflecting means is substantially circularly polarized. " Another optical system may be disposed between the light source and the quarter-wave plate, and even if the laser light flux from the light source is linearly polarized light, while passing through the other optical system, In some cases, the state changes from linearly polarized light to "elliptical polarized light having a single axis that is extremely short." In such a case, the polarization state after passing through the quarter-wave plate is not a strict circular polarization state. In the invention of claim 6, "substantially circularly polarized light" means
It is meant that such elliptically polarized light also includes the polarization state when transmitted through the quarter-wave plate.

An optical scanning device according to a ninth aspect is the optical scanning device described above, wherein "1 is provided on an optical path between the light source and the optical deflecting means.
A half wave plate was installed, and the direction of the main cross section of this half wave plate was set so that shading was reduced well. "
It is characterized by

In the optical scanning device according to the eighth or ninth aspect, one or more of the above-mentioned "mirrors for bending the optical path of the laser beam" can be provided between the optical deflecting means and the surface to be scanned. (Claim 10). The quarter wave plate and the half wave plate may be arranged at any positions between the light source and the deflective reflection surface.

An optical scanning device according to a eleventh aspect of the present invention is that "a semiconductor laser or a semiconductor laser array is used as a light source, a laser beam from the light source is deflected by an optical deflecting means having a deflecting reflection surface, and a surface to be scanned is scanned by a scanning lens. An optical scanning device in which one or more mirrors for bending the optical path of the laser beam are arranged between the optical deflecting means and the surface to be scanned, by performing light scanning by converging as a light spot.
"The inclination angle in one or more of these mirrors in the main scanning corresponding direction and / or the sub scanning corresponding direction is set so as to reduce shading well".

Also in the optical scanning device according to claim 5 or 10, the same as the optical scanning device according to claim 11,
"Shading of the tilt angle in the main scanning-corresponding direction and / or the sub-scanning-corresponding direction in one or more of the mirrors arranged to bend the optical path of the laser beam between the light deflecting unit and the surface to be scanned is reduced well. Can be set ”(claim 12).

[0017]

Referring to FIG. 1A, the laser light flux emitted from the laser light source 1 passes through the condenser lens 2, the aperture 3, and the cylinder lens 4 for the sub-scanning corresponding direction (see FIG. (A direction orthogonal to the drawing)), a focusing tendency is given, and an image is formed at the position of the deflective reflecting surface 5 as a long line image in the main scanning corresponding direction. The laser beam reflected by the deflecting / reflecting surface 5 is deflected as the deflecting / reflecting surface 5 rotates,
The light enters the scanning lens 6. The deflected laser beam that has passed through the scanning lens 6 has a mirror 7 for bending the optical path.
Is reflected by the light beam, the optical path is bent, the light beam is condensed as a light spot on the scanned surface 9 through the cover glass 8 of the optical scanning device, and the scanned surface 9 is optically scanned. A surface of the photosensitive member or the like is provided on the surface 9 to be scanned.

The condensing lens 2 may be a collimating lens for collimating the laser light flux from the laser light source 1 or a laser light flux having a converging tendency, or conversely, a slightly divergent light flux. May be In the illustrated example, the condenser lens 2 is a collimating lens. The aperture 3 is for setting the shape of the light spot on the surface 9 to be scanned. The cylinder lens 4 is for correcting the surface tilt of the deflecting / reflecting surface 5, and is not necessary when the deflecting / reflecting surface has no surface tilt or when performing another kind of surface tilt correction.

The deflecting / reflecting surface 5 is a reflecting surface of the light deflecting means, and is for reflecting the laser light beam and for deflecting the reflected laser light beam by rotating or swinging. As a light deflecting means having a rotatable deflecting / reflecting surface, a rotating polygon mirror,
A rotating two-sided mirror, a so-called hoso-type mirror, or the like can be used, and a galvanometer mirror can be used as the oscillating deflecting / reflecting surface. In the illustrated example, the light deflecting means is a rotating polygon mirror.

The scanning lens 6 is a lens for converging the deflected laser light flux as a light spot on the surface to be scanned, and is generally an fθ lens when the light deflecting means has a rotatable deflective reflection surface. If it has an oscillating deflecting / reflecting surface, an fsin θ lens is used. When the constant velocity of optical scanning is performed by electrical correction, the scanning lens may be a normal imaging lens. In the illustrated example, the scanning lens 6 is an anamorphic fθ lens, and the position of the deflective reflection surface 5 and the position of the scanned surface 9 have a geometrical optical conjugate relationship with respect to the sub-scanning corresponding direction, and the cylinder lens 4 The collapsing of the deflective reflection surface is corrected in cooperation with. The cylinder lens 4 is used to correct the tilt of the deflective reflection surface.
Alternatively, a long cylinder lens or toroidal lens may be used "as a part of the scanning lens" and these long lenses may be arranged near the surface to be scanned.

The mirror 7 is for bending the optical path of the deflected laser beam, and is usually provided in many cases depending on the layout requirements of the apparatus. Therefore, the mirror 7 can be omitted. However, in the optical scanning device according to claims 5, 9 and 10, this type of mirror is positively used to reduce shading. Further, the cover glass 8 is for dust-proofing of the optical scanning device.

Next, the light source 1 will be described. In the optical scanning device of the present invention, a semiconductor laser or a semiconductor laser array is used as the light source. As shown in FIG. 1B, the semiconductor laser 1A has a rectangular minute light emitting portion L0, and the emitted laser light is emitted from the light emitting portion L0.
It is substantially linearly polarized light with the longitudinal direction of 0 as the polarization direction. The far-field pattern of the emitted laser beam has an elliptical shape with the uniaxial direction as the polarization direction as shown by the chain line, and in order to improve the light utilization efficiency, the polarization direction is usually set to the sub-scanning corresponding direction. Deployed in parallel. The optical scanning mode in which the optical scanning is performed in such a manner that the polarization direction of the light source is substantially parallel to the sub-scanning corresponding direction is referred to as “A mode”.

As shown in FIG. 1C, the semiconductor laser array 1B has a plurality of laser emitting portions L1, L2, L.
3. ． Has a monolithic structure in which an array is arranged in one row at equal intervals along the joint surface. In this case, the polarization direction of the laser light flux from each light emitting unit is parallel to the array direction. When the semiconductor laser array is used as a light source, the number of lines equal to the number of light emitting parts can be optically scanned at one time.

When the semiconductor laser array 1B is used as the light source 1, it can be considered that the array direction (arrangement direction of the light emitting portions) is used in parallel with the sub-scanning corresponding direction. In this case, the optical scanning mode is the A mode. However, when the semiconductor laser array 1B is used as a light source to perform optical scanning in the A mode, generally, the intervals between lines that are simultaneously scanned become large, and high-density optical scanning is performed in the sub-scanning direction. Is not easy. For this reason,
As shown in (C), the array direction of the semiconductor laser array 1B is a minute angle θ (about 5 degrees) with respect to the main scanning corresponding direction.
It is generally used to be tilted and used as a light source.
In this case, the arrangement interval of the light emitting units in the light source unit is d · sin θ (d is the arrangement pitch of the light emitting units) in the sub-scanning corresponding direction, so that the interval between the adjacent lines in the optical scanning can be reduced.

When the semiconductor laser array is used in such an arrangement, the polarization direction of the laser beam emitted from the light source 1 is substantially parallel to the main scanning corresponding direction. The optical scanning mode in which the optical scanning is performed by making the polarization direction of the laser beam emitted from the light source substantially parallel to the main scanning corresponding direction is called "B mode".

Shading is generally
It occurs so that the light intensity of the light spot decreases toward the both ends in the main scanning direction, and the light intensity of the light spot increases in the B mode as it approaches the both ends in the main scanning direction.

Although the respective parts of the optical scanning device and the optical scanning mode have been described above, the present invention can be widely applied to the optical scanning devices and the optical scanning modes.

Now, in a medium having a refractive index of n ₀ , light is incident on the surface of a medium having a refractive index of n ₁ at an incident angle ψ, part of which is reflected and part of which is refracted at a refraction angle χ. In this case, the well-known Snell's formula: n ₀ sin ψ = n ₁ sin χ (1) holds between the incident angle ψ and the refraction angle χ. At this time, for P-polarized light and S-polarized light,
Amplitude reflectance at the boundary surface: rp, rs, amplitude transmittance:
tp and ts are rp = tan (ψ−χ) / tan (ψ + χ) (2) rs = −sin (ψ−χ) / sin (ψ + χ) (3) tp = 2sinχcosψ / {sin (ψ + χ) · cos, respectively. (Ψ−χ)} (4) ts = 2sin χcos ψ / {sin (ψ + χ)} (5)

Further, the energy reflectances Rp and Rs and the energy transmittances Tp and T for the P-polarized light and the S-polarized light, respectively.
s is Rp = | rp | ² (6) Rs = | rs | ² (7) Tp = {(cosχ · sinψ} / (cosψ · sinχ)} |, using rp, rs, tp, and ts, respectively. tp | ² (8) Ts = {(cos χ · sin ψ} / (cos ψ · sin χ)} | ts | ² (9)

Furthermore, refractive index: the surface of the n ₂ of the medium, the refractive index: coating layer of n ₁ is formed to a thickness d _1, this coating layer, the optical refractive index: incidence in the medium of n ₀ Energy reflectance: Rp, Rs and energy transmittance: Tp,
Ts ^{_{is, Rp = rp 01 2 + 2rp}} 12 · rp 12 · cos2δ 1 + rp 12 2 / {1 + rp 01 · rp 12 · cos2δ 1 + rp 01 2 · rp 12 2} (10) Rs = rs 01 2 + 2rs 12 · rs 12・ Cos2δ ₁ + rs ₁₂ ² / {1 + rs ₀₁・ rs ₁₂・ cos 2δ ₁ + rs ₀₂ ²・ rs ₁₂ ² } (11) Tp = n ₂・ tp ₀₁ ²・ tp ₁₂ ² / n ₀ (1 + 2rp ₀₁・ rp ₁₂・ cos ² δ ₁ + rp ₀₁ ² · rp ₁₂ ² } (12) Ts = n ₂ · ts ₀₁ ² · ts ₁₂ ² / n ₀ (1 + 2rs ₀₁ · rs ₁₂ · cos ² δ ₁ + rs ₀₁ ² · rs ₁₂ ² } (13 ), Rp ₀₁ , rs ₀₁ , tp ₀₁ , and ts ₀₁ are the refractive indices n ₀ for P-polarized light and S-polarized light, respectively.
Amplitude reflectance and amplitude transmittance between the medium and the coating layer,
It is calculated by the above (2) to (5). Similarly rp ₁₂ ,
rs ₁₂ , tp ₁₂ , and ts ₁₂ are amplitude reflectance and amplitude transmittance between the medium having a refractive index of n ₂ and the coat layer for P-polarized light and S-polarized light, respectively, and are (2) to (5) above. ). The phase δ ₁ is δ ₁ = (2π / λ)
It is given by n ₁ · d ₁ · cos χ (λ is the wavelength). When the coat layers are formed in multiple layers, Rp, Tp, Rs, and Ts can be obtained by sequentially applying the above relationships one by one.

The amplitude reflectance and the amplitude transmittance, which are the basis of the calculation of the energy reflectance and the energy transmittance, depend on the incident angle for both P-polarized light and S-polarized light. Therefore, if the incident angle changes, , Both reflectance and transmittance change.

Referring to FIG. 1A, in the configuration of the optical scanning device shown in FIG. 1, the optical element in which the incident angle of the laser beam changes within one main scanning is the deflective reflection surface 5, the scanning lens 6, and the optical path bending. For the mirror 7 and the cover glass 8. Among these, in the deflective reflection surface 5 and the mirror 7, the change of the reflectance with the change of the incident angle becomes a problem, and in the scanning lens 6 and the cover glass 8, the transmittance with the change of the incident angle. Change becomes a problem. Although the cover glass 8 is a parallel plate glass, both sides of the cover glass 8 are “refractive surfaces” because the refraction angle changes with the change of the incident angle.

First, considering the occurrence of shading due to the change in transmittance with the change in incident angle, in this case, the most significant effect on the occurrence of shading is the change in transmittance on the surface with the greatest change in incident angle due to optical scanning. Is.
In view of this, in the invention described in claim 1, "of the optical element surfaces which are arranged on the optical path from the light deflecting means to the surface to be scanned and which transmit the laser beam, the incident angle changes the most with the deflection of the laser beam. By providing an antireflection coat only on the refracting surface, the shading is reduced.

According to the second aspect of the present invention, "An antireflection coating is provided on one or more lens surfaces of the scanning lens, and the transmittance of the scanning lens gradually increases from the optical axis toward both ends in the main scanning corresponding direction. "Provided" to reduce shading. As described above, there is a general tendency that the shading and the light intensity of the light spot become smaller on both end sides in the main scanning direction than the central image height. Therefore, the above general tendency of shading can be offset by "increasing the transmittance of the scanning lens from the optical axis toward both ends in the main scanning corresponding direction".

In order to increase the transmittance of the scanning lens from the optical axis toward both ends in the main scanning corresponding direction by means of the antireflection coating, as in the invention according to claim 3, "the optimum film for the wavelength of the laser light beam is provided. There is a method to set the thickness thicker than the thickness. The antireflection effect of the antireflection coating varies depending on the thickness of the antireflection coating, and there is an optimum thickness according to the wavelength of the incident laser beam, but if the antireflection coating is formed to this optimum thickness, it will be compatible with main scanning. When the angle of incidence increases toward both ends in the direction, the antireflection effect tends to decrease. However, if the film thickness of the antireflection coat is set to be larger than the above optimum thickness, the transmittance increases with an increase in the incident angle, and the decrease in the antireflection function can be prevented.

According to a fourth aspect of the present invention, "The film thickness of the antireflection coating provided on one or more lens surfaces of the scanning lens is set to the lens optical axis portion (the optimum film thickness is set at the optical axis portion). Even if it is set so as to gradually thicken toward both ends in the main scanning corresponding direction, the transmittance increases as the incident angle increases, and the decrease in the antireflection function can be prevented.

According to a fifth aspect of the present invention, "One or more mirrors for bending the optical path of the deflected laser beam are provided with a reflection enhancing coat on the mirror surface thereof so that the reflectance is directed from the center to both ends in the main scanning corresponding direction. And gradually increase. ”
This also makes it possible to correct the decrease in the transmittance of the scanning lens or the like. In this case, as in the invention of claim 6, the thickness of the reflection film may be set to be “thicker gradually from the scanning corresponding direction to both ends”, or as in the invention of claim 7, The film thickness of the coat may be set to "thicker than the optimum film thickness for the wavelength of the laser beam".

Next, in the invention described in claims 8 to 10, the shading is reduced by using the wave plate. As shown in the equations (1) to (13) above, the reflectance / transmittance changes according to the incident angle ψ.
Polarized light and S-polarized light are different from each other. As a typical example, the correspondence relationship between the incident angle and the reflectance on the deflective reflection surface 5 and
The correspondence relationship between the incident angle and the transmittance on the first surface of the scanning lens 6 is shown in FIGS. In the figure, P
There is P polarization, and S is S polarization. First, the correspondence relationship between the reflectance and the incident angle will be described. In FIG. 2A, the “deflection region” is
A region in which the incident angle changes for deflecting the laser beam by the deflecting / reflecting surface 5 to perform main scanning is shown. As shown,
Within this deflection region, the reflectance of S-polarized light tends to increase with the incident angle, and the reflectance of P-polarized light tends to decrease with the increase of the incident angle.

In the above-mentioned A mode, in FIG. 1A, the polarization direction of the laser light emitted from the light source 1 is parallel to the sub-scanning corresponding direction.
The polarization state of the laser light beam incident on is the S polarization state. Therefore, when optical scanning is performed in the A mode, the change in the reflectance on the deflective reflection surface 5 changes from the start point to the end point of the main scanning of the light spot. This causes shading that increases the intensity, which is the reverse of the above in the B mode. The correspondence between the reflectance and the incident angle is qualitatively the same as that shown in FIG.

On the other hand, in FIG. 2 (B) showing the correspondence between the transmittance and the incident angle, the main scanning region is the optical axis (incident angle: 0) of the scanning lens and the end of the main scanning region. This is the range of the incident angle of the laser beam when scanning, and the actual main scanning area is symmetrical with respect to the optical axis. As is apparent from the figure, the transmittance of P-polarized light gradually increases from the optical axis position toward the end of the main scanning region, and the transmittance of S-polarized light gradually decreases. This tendency is common.

In FIG. 2, the broken line curve indicates the reflectance / transmittance for circularly polarized light. As shown in the figure, the reflectance / transmittance of circularly polarized light is substantially stable in the polarization region / main scanning region.
Therefore, if the laser light flux incident on the deflecting / reflecting surface 5 is circularly polarized light, the reflectance / transmittance changes on the optical path from the deflecting / reflecting surface to the scanned surface regardless of the A mode / B mode. Is effectively reduced, and shading can be reduced. Therefore, in the invention described in claim 8, a quarter wavelength plate is provided between the light source and the deflective reflection surface so that the laser light flux incident on the deflective reflection surface becomes substantially circularly polarized light. is there.

Even if the light incident on the reflecting surface / transmitting surface is linearly polarized light, the incident laser light is P-polarized to the reflecting surface / transmitting surface if the direction of polarization is inclined with respect to the incident surface. Component and S polarization component, the reflectance and transmittance of each of these P and S polarization components behave similarly to the P polarization and S polarization shown in FIG. The P and S polarization components are mixed together, the transmission and reflection characteristics of the P and S polarizations are canceled out, the fluctuation is small with respect to the incident angle change, and shading is reduced.

Therefore, according to the invention of claim 9, "a half-wave plate is provided between the light source and the deflecting / reflecting surface so that the laser beam incident on the deflecting / reflecting surface has both S and P polarized components. Have it.

FIG. 3 shows the half-wave plate 14.
The "main cross section" 14A coincides with the optical axis direction of the crystal. When the light polarized in the direction of the main cross section 14A as shown by the solid line arrow (the polarization direction forms an angle η with the main cross section 14A) is transmitted, the polarization plane of the transmitted light is indicated by the "broken line arrow". like,
It rotates by an angle of 2η with respect to the plane of polarization of the incident light. Therefore, in both the A mode and the B mode, the polarization plane of the laser light flux incident on the deflecting / reflecting surface is swung by using the ½ wavelength plate, so that the reflecting surface and the refracting surface after the deflecting / reflecting surface are rotated. Thus, S-polarized light and P-polarized light can be mixed. In this case, as in the tenth aspect of the invention, by using one or more mirrors for bending the optical path between the light deflecting means and the surface to be scanned, the transmission / transmission of the P and S deflections is performed.
The offset adjustment of the reflection characteristics becomes easy.

The quarter wave plate and the half wave plate may be arranged at any positions between the light source and the deflection means. For example, between the light source and the condenser lens, the condenser lens and the cylinder lens. Or between the cylinder lens and the deflective reflection surface. When a quarter wave plate or a half wave plate is provided between the light source and the condenser lens, these wave plates may be used as the cover glass of the package of the semiconductor laser or the semiconductor laser array which is the light source. ..

Alternatively, each of the two wavelength plates may be "integrated with the lens cell of the condensing lens on the entrance side or the exit side of the condensing lens", and in contact with the entrance surface or the exit surface of the cylinder lens. May be deployed.

Further, in the inventions of claims 11 and 12, one or more mirrors for bending the optical path of the deflected laser beam are arranged between the deflective reflection surface and the surface to be scanned, and the tilt angles of these mirrors are adjusted. To reduce shading.

According to the eleventh aspect of the present invention, the shading is reduced only by adjusting the tilt of the mirror. In the twelfth aspect of the invention, in addition to the tilt adjustment of the mirror,
The above-mentioned antireflection coating, increased reflection coating, or wave plate is used in combination to reduce shading. As a mode of tilting the mirror, there are a tilting method in which the mirror is tilted in the sub scanning corresponding direction, a tilting method in which the mirror is tilted in the main scanning corresponding direction, and a tilting method in which the mirror is tilted in the sub scanning corresponding direction and the main scanning corresponding direction.

In order to explain this tilting method, "polarization plane"
And consider the "plane orthogonal to the polarization". Assuming that the optical axis of the scanning lens is linearly expanded from the polarization plane to the scanned surface, and in this state, the plane deflected by the principal ray of the laser beam ideally deflected by the deflection reflection surface is deflected. A surface including the optical axis and orthogonal to the deflection surface is referred to as a plane orthogonal to the plane. The tilting of the mirror in the sub-scanning corresponding direction means that the normal line standing on the mirror surface of the mirror tilts with respect to the optical axis in the plane orthogonal to the deflection. Further, tilting the mirror in the main scanning corresponding direction means that the normal line is tilted with respect to the optical axis in the deflection plane, and tilting in the main scanning corresponding direction and the sub scanning corresponding direction means the above two directions. Says to combine inclinations.

FIG. 4A shows an optical arrangement of the optical scanning device in FIG. 1A from the deflective reflection surface 5 to the scanned surface 9 in the plane orthogonal to the deflection. The mirror 7 is arranged so as to be inclined by an angle α in the sub-scanning corresponding direction. now,
If the angle at which the deflected laser light beam is incident on the mirror 7 in the deflection plane is β, in this state, the angle φ formed by the deflected laser beam with respect to the normal line of the mirror 7 (that is, the incident angle on the mirror 7). , said alpha, using beta, is given by ^{φ = cos ~ 1 (cosα ·} cosβ) (14). When the deflection laser beam is linearly deflected, and at an incident angle φ, the angle between the incident surface and the direction of linear deflection is θ, the reflectance by the mirror is R
Using p, Rs and θ, it is given by R = √ {(Rp · cos θ) ² + (Rs · sin θ) ² } (15).

For example, in the case where the mirror 7 is an aluminum mirror provided with a high-reflectance coating, the reflectances of P-polarized light and S-polarized light are shown in FIG.
Changes like curves P and S in FIG. Now, assuming that the tilt angle β of the mirror 7 shown in FIG. 4 is 45 degrees, the incident angle of the polarized laser light flux entering the mirror 7 due to the polarization of the laser beam: φ is on the optical axis of the scanning lens. It is 45 degrees, and the incident angle: φ increases as the deflection angle increases.

First, considering the A mode as the optical scanning mode, in this case, the polarization direction of the deflected laser beam is as shown in FIG.
In (A), it is parallel to the drawing and is the vertical direction of the drawing. Therefore, the polarized laser light flux enters the mirror 7 as P-polarized light at an incident angle of 45 degrees on the optical axis of the scanning lens 6.
Therefore, the reflectance on the optical axis is point a in FIG. However, as the deflection angle increases, the incident angle on the mirror 7 also increases. At this time, the P-polarized component incident on the mirror 7 gradually decreases, while the S-polarized component gradually increases. Therefore, the reflectance gradually increases from point a to point c in FIG. 4A as the deflection angle increases. As mentioned above, in A mode, shading is
Since the light intensity of the light spot tends to gradually decrease toward both ends in the main scanning direction, the increase of the reflectance by the mirror 7 can suppress the light intensity variation of the light spot and effectively reduce shading. ..

In the B mode, the reflectance of the mirror 7 on the optical axis of the scanning lens is point b in FIG. 4 (B), but the P polarization component increases as the deflection angle increases. ,
The reflectance changes so as to slightly decrease toward point c.
In the B mode, since the light intensity of the light spot tends to be slightly stronger at both ends in the main scanning direction with respect to the image height of 0, the shading can be achieved by inclining the mirror 7 by an appropriate angle in the sub scanning corresponding direction. It can be effectively reduced.

Similarly, the shading can be reduced by inclining one or more of the mirrors for bending the optical path in the main scanning corresponding direction.

That is, usually, in the optical scanning optical system, since the laser beam is made incident on the deflective reflection surface 5 at a certain angle, on the starting side (-side) and the ending side (+ side) of the main scanning, The light intensities of the light spots are not equal. Therefore, by tilting the mirror 7 in the main scanning direction, it is possible to reduce the light amount difference between the image heights on the + side and the − side.

For example, in the A mode, the light having the reflectance on the deflective reflection surface is higher on the − side than on the + side. When the mirror 7 is also tilted in the main scanning direction, the + side has more S-polarized components than the − side, so the reflectance on the + side increases, and as a result, the difference in the amount of light between the + side and the − side is reduced, and shading is reduced. Is done.

[0057]

EXAMPLES Specific examples will be described below. The first embodiment described is an example in which the invention according to claim 1 is applied to the optical scanning device shown in FIG.

As described above, the feature of the invention according to claim 1 is that, among the optical element surfaces provided on the optical path from the light deflecting means to the surface to be scanned and transmitting the laser beam, The antireflection coating is provided only on the refracting surface where the incident angle changes the most with the deflection of the laser beam. " Before describing in detail, each interface (reflection surface / refraction) of the optical element from the deflective reflection surface 5 to the scanned surface 9 of the optical scanning device shown in FIG. Surface) and the reflectance and transmittance at these interfaces. First, regarding the deflecting / reflecting surface 5, an aluminum mirror surface is coated with SiO to a thickness of ½ of the used wavelength: 780 nm. The relationship between the incident angle and the reflectance of this deflective reflection surface is as shown in FIG. Each of the two lenses forming the scanning lens 6 is made of polycarbonate and has an uncoated surface. The relationship between the incident angle and the transmittance on each surface of these lenses is shown in FIG.
This is as shown in (B). Mirror 7 for bending the optical path
Has a high-reflective coat in which four layers of MgF ₂ thin films and TiO ₂ thin films (thicknesses are 1/4 of the used wavelength) are alternately laminated on the aluminum mirror surface. Cover glass 8
Is a plane-parallel glass plate, and the front and back surfaces are uncoated.

The angle of incidence on each of these reflecting / refracting surfaces is defined by the image height of the light spot on the surface to be scanned (the distance from the position corresponding to the optical axis of the scanning lens to the light spot measured in the main scanning direction; unit). mm) is shown below. As described above, α and β represent the incident projection angles of the light beam in the sub scanning corresponding direction and the main scanning corresponding direction, respectively. The unit of these incident projection angles is degrees.

Image height: -150 -100 -50 0 +50 +100 +150 Deflection / reflection surface α 52 45 37 30 23 16 8 β 0 0 0 0 0 0 0 Scanning lens first surface α 29 20 10 0 10 20 29 β 0 0 0 0 0 0 0 2nd surface α 16 11 6 0 6 11 16 β 0 0 0 0 0 0 0 3rd surface α 38 26 13 0 13 26 38 β 0 0 0 0 0 0 0 4th surface Surface α 1 2 2 0 2 2 1 β 0 0 0 0 0 0 0 Mirror for bending the optical path α 24 17 9 0 9 17 24 β 25 25 25 25 25 25 25 25 Cover glass 1st surface α 24 17 9 0 9 17 24 β 0 0 0 0 0 0 0 2nd surface α 24 17 9 0 9 17 24 β 0 0 0 0 0 0 0 From this, it is understood that the mirror 7 is tilted 25 degrees in the sub-scanning corresponding direction. Let's do it.

Next, the relation between the reflectance / transmittance at each interface and the image height is as follows. A and B represent optical scanning modes.

Image height: -150 -100 -50 0 +50 +100 +150 Deflection / reflection surface A 0.917 0.907 0.896 0.887 0.880 0.874 0.869 B 0.798 0.822 0.841 0.852 0.859 0.864 0.867 Scanning lens first surface A 0.931 0.942 0.949 0.951 0.949 0.942 0.931 B 0.967 0.958 0.952 0.951 0.952 0.958 0.967 Second surface A 0.945 0.948 0.951 0.951 0.951 0.948 0.945 B 0.955 0.953 0.951 0.951 0.951 0.953 0.955 Third surface A 0.913 0.936 0.947 0.951 0.947 0.936 0.913 B 0.978 0.964 0.954 0.951 0.954 0.964 0.978 Fourth Surface A 0.951 0.951 0.951 0.951 0.951 0.951 0.951 B 0.951 0.951 0.951 0.951 0.951 0.951 0.951 Mirror for optical path bending A 0.979 0.979 0.978 0.978 0.978 0.979 0.979 B 0.980 0.983 0.985 0.986 0.985 0.983 0.980 Cover glass 1st surface A 0.946 0.952 0.956 0.957 0.956 0.952 0.946 B 0.967 0.962 0.959 0.957 0.959 0.962 0.967 Second surface A 0.946 0.952 0.956 0.957 0.956 0.952 0.946 B 0.967 0.962 0.959 0.957 0.959 0.962 0.967 As a result, the light arrival efficiency on the scanned surface is , To B both modes, comprising as follows against concerning each image height.

Image height: -150 -100 -50 0 +50 +100 +150 Light arrival efficiency A 0.614 0.640 0.651 0.650 0.639 0.616 0.582 B 0.682 0.626 0.626 0.629 0.639 0.658 0.682 Using this light arrival efficiency, for each of the above image heights If the shading amount is defined by {(light arrival efficiency at image height) / (maximum light arrival efficiency) -1} × 100 (%), the shading amount at each image height described above corresponds to each of A and B light scanning modes. , As follows.

Shading amount Image height: -150 -100 -50 0 +50 +100 +150 A mode -5.7 -1.7 0 -0.2 -1.8 -5.4 -10.6 B mode -7.9 -8.2 -8.2 -7.8 -7.8 -3.5 As described above, in the A mode, the shading is small in the portion where the image height is small, and the shading increases as the image height increases. FIG. 5 shows how shading is performed in both A and B modes.

Now, looking at the change in the incident angle of the laser beam on each of the above interfaces, the refraction surface where the incident angle changes the most with the main scanning at these interfaces, the incident angle is ±
It is the third lens surface of the scanning lens 6, which changes by 38 degrees.

Embodiment 1 Therefore, in order to carry out the invention described in claim 1, FIG.
As shown in (A), an antireflection coating 1 is formed on the lens surface.
1 is set. In this embodiment, the antireflection coat 11
Is a thin film of Al ₂ O ₃ (refractive index: n ₁ = 1.63) directly on the third lens surface of the scanning lens, thickness: 141 nm
(Λ / (4n ₁ ); λ: wavelength used: 780 nm), and a thin film of MgF ₂ (refractive index: n ₂ = 1.3
8) is formed to a thickness of 120 nm (λ / (4n ₂ )). The above film thickness is an optimum value for the thickness of the antireflection film. The optical scanning mode is A mode.

With this antireflection coating 11, the transmittance of the third surface of the scanning lens 6 becomes as follows for each image height. Image height: -150 -100 -50 0 +50 +100 +150 Transmittance Third surface of scanning lens 0.991 0.998 1.000 1.000 1.000 0.998 0.991 The relationship between the incident angle and the reflectance is shown in FIG. 6 (A). In the range of the incident angle fluctuation range of ± 38 degrees, the change in reflectance is small for both S and P polarized lights.

The shading amount when the reflection film 11 is provided and the optical scanning is performed in the A mode is as follows for each image height. Shading amount Image height: -150 -100 -50 0 +50 +100 +150 A mode -3.1 -0.7 0 -0.6 -1.7 -4.4 -8.2 The state of this shading is shown by the broken line in FIG. 6 (B).
It can be seen that the shading is obviously improved as compared with the state of shading in the case where the antireflection coat 11 is not provided, which is shown by the solid line in FIG.

Embodiment 2 Embodiment 2 is an embodiment of the invention of claim 3. In the first embodiment, the film thickness of the antireflection coat formed on the third surface of the scanning lens 6 is set to the optimum value. In this second embodiment,
The thickness of the antireflection coat is set to be larger than the optimum value. That is, as in Example 1, when the antireflection coating is formed as a two-layer film having a refractive index of n ₁ and n ₂ ,
As described above, the film thicknesses d ₁ and d ₂ of the respective layers are d ₁ = λ / (4
n ₁ ), d ₂ = λ / (4n ₂ ), but in the invention of claim 3, these d ₁ and d ₂ are d ₁ > λ / (4n ₁ ) d ₂
> Λ / (4n ₂ ).

The Al ₂ O ₃ thin film in Example 1 was formed to a thickness of 172 nm, and the MgF ₂ thin film formed thereon had a thickness of 146 nm. At this time, the transmittance of the third surface of the scanning lens 6 for each image height was as follows for each image height. Image height: -150 -100 -50 0 +50 +100 +150 Transmittance Third lens surface for scanning 0.991 0.987 0.985 0.984 0.985 0.987 0.991 The relationship between the incident angle and the reflectance is shown in FIG. 7 (A). In the range of the incident angle variation range of ± 38 degrees, the change in reflectance is small for both S and P polarized light, and the transmittance increases as the incident angle increases.

By providing the antireflection coat 11 having the above-mentioned thickness,
The shading amount when optical scanning is performed in A mode is
It became as follows for each image height. Shading amount Image height: -150 -100 -50 0 +50 +100 +150 A mode -1.6 -0.3 0 -0.7 -1.8 -4.0 -6.8 The state of this shading is shown by the broken line in FIG. 7 (B).
It can be seen that the shading is further improved in comparison with the shading state of the first embodiment shown by the broken line in FIG.

As a modification of the second embodiment, the thickness of each layer of the antireflection coating is set to a thickness at which the optimum antireflection effect can be obtained at an incident angle of 0 degree on the optical axis, and at both ends in the main scanning corresponding direction, The thickness may be set so as to obtain the optimum antireflection effect at an incident angle of 38 degrees, and the film thickness may be gradually increased from the central portion toward both end portions (claim 4). It is also applicable to the cover glass 8 that the antireflection coating is provided and that the film thickness is set so that the transmittance at both end portions is higher than the central portion in the main scanning corresponding direction.

Embodiment 3 Embodiment 3 is an embodiment of the invention of claims 5 and 7, and is shown in FIG.
In the optical scanning device shown in (A), the film thickness of the reflection-increasing coating 12 formed on the mirror surface of the mirror 7 for bending the optical path is set to be larger than the optimum film thickness.

On the aluminum mirror surface of the mirror 7, MgF
The thin film of ₂ (refractive index: n ₃ = 1.38) and the thin film of TiO ₂ (refractive index: n ₄ = 2.35) are alternately formed into 4 layers, and from the aluminum mirror surface side toward the air region, The MgF ₂ thin film, the TiO ₂ thin film, the MgF ₂ thin film, and the TiO ₂ thin film are stacked in this order. At this time, the optimum film thickness of the MgF ₂ thin film and the TiO ₂ thin film is the wavelength used: λ = 7
For 80 nm, d ₃ = λ / (4n ₃ ) = 83, respectively
nm, d ₄ = λ / (4n ₄ ) = 141 nm, but in the invention of claim 7, these film thicknesses: d ₃ , d ₄ are changed to d ₃
> Λ / (4n ₃ ), d ₄ > λ / (4n ₄ ). In Example 3, these film thicknesses were respectively set to d ₃ =
It was set to 101 nm and d ₄ = 172 nm.

At this time, the reflectance of the mirror 7 for each image height was as follows for each image height. Image height: -150 -100 -50 0 +50 +100 +150 Reflectivity 0.960 0.952 0.944 0.940 0.944 0.952 0.960 The relationship between the incident angle and the reflectivity is shown in FIG. 8 (A). In the range of the incident angle variation range of 25 to 34 degrees, the reflectances of both S and P polarized light increase with the increase of the incident angle.

By providing the antireflection coating 12 having the above thickness,
The shading amount when the optical scanning is performed in the mode is as follows for each image height. Shading amount Image height: -150 -100 -50 0 +50 +100 +150 A mode -4.1 -1.0 0 -0.5 -1.8 -4.6 -9.2 The state of this shading is shown by the broken line in FIG. 8 (B).
The shading is improved as compared with the case where the enhanced reflection coat 12 is not used (the curve of the broken line).

As a modification of the third embodiment, the thickness of each layer of the reflection enhancing coating is set to a thickness at which an optimum reflection enhancing effect is obtained at an incident angle of 25 degrees on the optical axis, and at both ends in the main scanning corresponding direction, The thickness may be gradually increased from the central portion to both end portions so that the optimum reflection enhancing effect is obtained at an incident angle of 34 degrees (claim 6).

The fourth and fifth embodiments described below are claimed in claim 8.
In the embodiments of the invention described in Nos. 10 to 10, as shown in FIG. 1 (A), a wave plate 13 is arranged between the light source 1 and the deflective reflection surface 5. In the fourth embodiment, a quarter wave plate is used as the wave plate 13, and the laser light flux from the light source is incident on the deflective reflection surface as substantially circularly polarized light. In this case, since the P-polarized light component and the S-polarized light component are equally included in the laser light flux incident on the optical elements below the deflective reflection surface 5, the shading is performed regardless of whether the optical scanning mode is the A mode or the B mode. The state will be the same.

Example 4 As shown in FIG. 1A, when a quarter-wave plate is provided at the position of the wave plate 13, the reflectance / transmittance (A mode / B) at each interface below the deflective reflection surface is shown. Common to all modes)
For each image height, it became as follows.

Image height: -150 -100 -50 0 +50 +100 +150 Deflection / reflection surface 0.858 0.865 0.896 0.870 0.869 0.869 0.868 Scanning lens 1st surface 0.949 0.950 0.951 0.951 0.951 0.950 0.949 2nd surface 0.950 0.951 0.951 0.951 0.951 0.951 0.950 Third surface 0.946 0.950 0.950 0.951 0.950 0.950 0.946 Fourth surface 0.951 0.951 0.951 0.951 0.951 0.951 0.951 Mirror for optical path bending 0.980 0.981 0.982 0.982 0.982 0.981 0.980 Cover glass First surface 0.957 0.957 0.957 0.957 0.957 0.957 0.957 Second surface 0.957 0.957 0.957 0.957 0.957 0.957 0.957 The light arrival efficiency on the surface to be scanned is as follows for each image height in both A and B modes.

Image height: -150 -100 -50 0 +50 +100 +150 Light arrival efficiency 0.625 0.634 0.639 0.640 0.639 0.637 0.632 The shading amount is as follows in each of A and B modes.

Image height: -150 -100 -50 0 +50 +100 +150 Shading amount -2.3 -0.9 -0.2 0 -0.2 -0.5 -1.3 FIG. 9 shows the shading state. It can be seen that the use of the wave plate improves shading extremely regardless of the A and B modes.

Embodiment 5 As shown in FIG. 1 (A), a half-wave plate is provided at the position of the wave plate 13 and the polarization direction of the laser beam from the light source 1 is rotated 45 degrees from the initial polarization direction. Then, the light is made incident on the deflective reflection surface 5. Therefore, with respect to the deflection state of the laser light flux with respect to each optical element after the deflecting / reflecting surface 5, the P and S deflections are equivalent to each other, and the reflectance / transmittance at each interface is common to A mode / B mode and After getting high, it became as follows.

Image height: -150 -100 -50 0 +50 +100 +150 Deflection / reflection surface 0.858 0.865 0.896 0.870 0.869 0.869 0.868 Scanning lens 1st surface 0.949 0.950 0.951 0.951 0.951 0.950 0.949 2nd surface 0.950 0.951 0.951 0.951 0.951 0.951 0.950 Third surface 0.946 0.950 0.950 0.951 0.950 0.950 0.946 Fourth surface 0.951 0.951 0.951 0.951 0.951 0.951 0.951 Mirror for optical path bending 0.980 0.981 0.982 0.982 0.982 0.981 0.980 Cover glass First surface 0.957 0.957 0.957 0.957 0.957 0.957 0.957 Second surface 0.957 0.957 0.957 0.957 0.957 0.957 0.957 The light arrival efficiency on the surface to be scanned is as follows for each image height in both A and B modes.

Image height: -150 -100 -50 0 +50 +100 +150 Light arrival efficiency 0.625 0.634 0.639 0.640 0.639 0.637 0.632 The shading amount is as follows in each of A and B modes.

Image height: -150 -100 -50 0 +50 +100 +150 Shading amount -2.3 -0.9 -0.2 0 -0.2 -0.5 -1.3 That is, reflectance, transmittance, light arrival efficiency, and shading amount are This is exactly the same as in the case of the above-described fourth embodiment, and thus the shading is as shown in FIG.

The B mode in Examples 1 to 5 described above indicates optical scanning in a state in which the direction of the linearly polarized light of the laser beam emitted from the light source is made parallel to the sub-scanning corresponding direction. .. As described above, B-mode optical scanning,
Generally, a semiconductor laser array is used as the light source. However, when performing B-mode optical scanning using the semiconductor laser array, the polarization direction of the laser beam emitted from the light source generally corresponds to the main scanning as described above. Shading in this case is slightly different from that in the B mode in the above-described embodiment because it is inclined by a small angle of about 5 degrees.

Example 6 The mirror 7 was removed from the optical arrangement of the optical scanning device shown in FIG. 1A to form an optical scanning device as shown in FIG. 10A. In order to avoid complication, the same reference numerals as those in FIG. 1 (A) are used for those thought to have no possibility of confusion. Although not shown, the cover glass 8 is used.

When the wave plate 13 is not used, the image height is -14.
The light arrival efficiency and the shading amount at 7 mm, 0, and +147 mm were as follows.

Image height -147 0 +147 Light arrival efficiency 88.4 94.3 100 Shading amount -11.6 -5.8 0.

On the other hand, in the sixth embodiment, 1/2
A wave plate is used as the wave plate 13, and the direction of the main cross section is
The polarization of the laser light flux which is set at 20 degrees with respect to the polarization direction of the laser light flux from the light source (semiconductor laser array, the array direction is tilted 5 degrees with respect to the main scanning corresponding direction) and is incident on the deflective reflection surface 5. The direction is inclined by 45 degrees with respect to the main scanning corresponding direction. As a result, the light arrival efficiency and the shading amount for each image height are as follows.

Image height -147 0 +147 Light arrival efficiency 93.8 100 96 Shading amount -6.2 0 -4.2.

The state of shading is shown in FIG. It can be seen that the use of the half-wave plate effectively reduces shading.

Example 7 In the optical arrangement of the optical scanning device shown in FIG. 1A, a semiconductor laser array was used as a light source, the array direction was tilted 5 degrees with respect to the main scanning corresponding direction, and 1 / When a two-wave plate was used and the inclination of the main cross section thereof was adjusted so as to reduce shading most, the shading was as shown in FIG. In addition, the mirror 7 was arranged at a 45 ° angle in the sub-scanning corresponding direction.

As a modification, the cylinder lens 4 is removed from the optical scanning device shown in FIG. 12 (the optical scanning device shown in FIG. 1A), and a long length for surface tilt correction is provided near the surface 9 to be scanned. A cylinder lens 15 is arranged as shown in FIG.
The scanning lens 6 in the sub-scanning direction is an anamorphic lens in which the position of the deflective reflection surface and the position of the surface to be scanned have a geometrical-optical conjugate relationship in the sub-scanning corresponding direction, but in the optical system of FIG. Since the polarized laser light flux is a parallel light flux, the scanning lens 6A is not an anamorphic one) and the direction of the main cross section of the half-wave plate 13 can be adjusted to effectively reduce shading. It was

Returning to FIG. 1A, the wave plate 13 (1/2
As described above, the wavelength plate or the quarter-wave plate) may be arranged at any position between the light source 1 and the deflective reflection surface 5, between the light source 1 and the condenser lens 2, and between the condenser lens 2 and the condenser lens 2. Any portion between the aperture 3 and the aperture 3 and the cylinder lens 4 (in the case of FIG. 1A) or between the cylinder lens 4 and the deflecting / reflecting surface 5 may be used, or the semiconductor laser which is the light source 1. Alternatively, it may be integrated with the cover glass on the laser beam emitting side of the package of the semiconductor laser array, or it may be integrated with the lens barrel of the condenser lens 2, and the wave plate 13 is in contact with the cylinder lens 4. It can also be provided.

Below, several specific examples of the arrangement of the wave plate will be described, taking the case where the wave plate 13 is a half wave plate as an example. When the half-wave plate is used, the direction of the main cross section is adjusted, so that it must be rotatably provided.

FIG. 13 shows an example in which the half-wave plate 13 is integrated with the lens barrel 31 of the condenser lens 2.

A tooth profile 7 is formed on a part of the outer circumference of the half-wave plate 13.
G is formed, and the whole is rotatably surrounded by the immovable member 72. A screw 70 is meshed with the tooth profile 7G, and is rotatably supported by means (not shown) without displacement. The half-wave plate 13 can be rotated by rotating the screw 70.
In this example, since the half-wave plate 13 and the lens barrel 31 are integrated with each other, when the half-wave plate 13 is rotated as described above, the lens barrel 31 is also integrated and is rotated around the optical axis. Rotate.

In FIG. 14, the half-wave plate 13 is integrated with the cover glass of the package 30 of the semiconductor laser array which is the light source. In the example, package 3
0 is fixed to the immovable member and does not move. The emitting portion of the laser beam is formed in a cylindrical shape and a cover glass is provided at the end thereof, but instead of this, a ½ wavelength plate 13 is rotatably fitted. As in the example of FIG. 13, screws 7
By rotating 0, the direction of the main cross section can be adjusted.

FIGS. 15A, 15B and 15C show a method of disposing the half-wave plate 13 in close contact with the cylinder lens 4. 15A is a side view, and FIG. 15B is a view seen from the optical axis direction. A holding portion 17A is formed on the lens holder 17. The holding portion 17A contacts the flat lens surface of the cylinder lens 4 on the one hand, and forms a pocket-shaped holding space together with this lens surface. The half-wave plate 13 is inserted into this holding space, and the cylinder lens 4 and the holding portion 17A are fixed by a pair of leaf springs 19A and 19B. The knob 14 formed on the half-wave plate 13
The 1/2 wavelength plate 13 is oscillated by A1 to adjust the direction of the main cross section.

In this example, the half-wave plate 13 is arranged on the flat lens surface side of the cylinder lens.
As shown in (C), it may be placed in close contact with a cylindrical surface. In this way, close to the lens surface 1/2
When the wave plate is provided, the device space can be used more effectively than when the 1/2 wave plate is provided at its own position.

[0103]

As described above, according to the present invention, a novel optical scanning device can be provided. Since the optical scanning device of the present invention is configured as described above, it is possible to effectively perform shading based on the relationship between the polarization direction of the laser light emitted from the semiconductor laser or the semiconductor laser array which is the light source and the optical scanning optical system. It is possible to reduce the number and realize good optical scanning.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an optical scanning device of the present invention.

FIG. 2 is a diagram for explaining how reflectance and transmittance change with incident angle for P and S polarized light.

FIG. 3 is a diagram for explaining a half-wave plate.

FIG. 4 is a diagram for explaining the influence of a mirror for bending an optical path on shading.

FIG. 5 is a diagram showing how shading is performed in A-mode optical scanning and B-mode optical scanning.

FIG. 6 is a diagram for explaining the effect of the first embodiment.

FIG. 7 is a diagram for explaining the effect of the second embodiment.

FIG. 8 is a diagram for explaining the effect of the third embodiment.

FIG. 9 is a diagram for explaining effects of Examples 4 and 5.

FIG. 10 is a diagram for explaining the sixth embodiment and the effect thereof.

FIG. 11 is a diagram for explaining the effect of the seventh embodiment.

FIG. 12 is a diagram showing a modified optical arrangement of an optical scanning device to which the present invention can be applied.

FIG. 13 is a diagram showing an example in which a half-wave plate is integrated with a lens barrel of a condenser lens.

FIG. 14 is a diagram showing an example in which a half-wave plate is integrated with a package of a semiconductor laser array.

FIG. 15 is a diagram for explaining an example in which a half-wave plate is arranged in contact with a cylinder lens.

[Explanation of symbols]

1 Light source (semiconductor laser or semiconductor laser array) 2 Condensing lens 3 Aperture 4 Cylinder lens 5 Deflection / reflection surface 6 Scanning lens 7 Optical path bending mirror 8 Cover glass 9 Scanned surface 11 Antireflection coating 12 Increased reflection coating 13 Wavelength Plate (1/2 wave plate or 1/4 wave plate)

Continuation of front page (31) Priority claim number Japanese Patent Application No. 4-36500 (32) Priority Day 4 (1992) February 24 (33) Priority claim country Japan (JP)

Claims (12)

[Claims] 1. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting reflection surface, and is condensed as a light spot on a surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, the incident angle changes the most along with the deflection of the laser light beam on the optical element surface that is provided on the optical path from the light deflection means to the scanned surface and transmits the laser light beam. An optical scanning device with reduced shading, characterized in that an antireflection coating is provided only on the refracting surface. 2. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting and reflecting surface, and is condensed as a light spot on the surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, an antireflection coating is provided on one or more lens surfaces of the scanning lens,
An optical scanning device with reduced shading, characterized in that the transmittance of a scanning lens is provided so as to gradually increase from the optical axis toward both ends in the main scanning corresponding direction. 3. The optical scanning device according to claim 2, wherein the film thickness of the antireflection coating provided on one or more lens surfaces of the scanning lens is set to be thicker than the optimum film thickness for the wavelength of the laser beam. An optical scanning device with reduced shading, which is characterized in that 4. The optical scanning device according to claim 2, wherein the film thickness of the antireflection coating provided on one or more lens surfaces of the scanning lens is directed from the lens optical axis portion toward both end sides in the main scanning corresponding direction. The optical scanning device with reduced shading is characterized in that the thickness is gradually increased. 5. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting and reflecting surface, and is condensed as a light spot on the surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, one or more mirrors for bending an optical path of a laser beam are provided between a light deflecting unit and a surface to be scanned, and a reflection-increasing coat is provided on the mirror surface of one or more mirrors for reflection. An optical scanning device with reduced shading, characterized in that the rate is gradually increased from the central portion in the main scanning corresponding direction to both end portions. 6. The optical scanning device according to claim 5, wherein the film thickness of the increased reflection coating gradually increases from the main scanning corresponding direction toward both ends.
Optical scanning device with reduced shading. 7. The optical scanning device according to claim 5, wherein the film thickness of the enhanced reflection coating is set to be thicker than the optimum film thickness for the wavelength of the laser beam. .. 8. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting and reflecting surface, and is condensed as a light spot on the surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, a quarter wavelength plate is provided on the optical path between the light source and the light deflecting means so that the laser light flux incident on the light deflecting means becomes substantially circularly polarized light. An optical scanning device with reduced shading. 9. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting reflection surface, and is condensed as a light spot on the surface to be scanned by a scanning lens. In an optical scanning device that performs optical scanning, a half-wave plate is provided on the optical path between a light source and a light deflector, and the direction of the main cross section of the half-wave plate is reduced so that shading can be reduced well. Is set to
Optical scanning device with reduced shading. 10. The optical scanning device according to claim 8 or 9, characterized in that one or more mirrors for bending the optical path of the laser beam are provided between the optical deflecting means and the surface to be scanned. Optical scanning device. 11. A semiconductor laser or a semiconductor laser array is used as a light source, a laser light flux from the light source is deflected by an optical deflecting means having a deflecting and reflecting surface, and is condensed as a light spot on the surface to be scanned by a scanning lens. In an optical scanning device for performing optical scanning, one or more mirrors for bending an optical path of a laser beam are provided between a light deflecting unit and a surface to be scanned, and main scanning corresponding directions in one or more of these mirrors and / or
Alternatively, the optical scanning device with reduced shading is characterized in that the inclination angle in the sub-scanning corresponding direction is set so as to reduce shading well. 12. The optical scanning device according to claim 5 or 10, wherein one or more mirrors arranged to bend the optical path of the laser beam between the optical deflecting means and the surface to be scanned,
An optical scanning device with reduced shading, wherein an inclination angle in a main scanning corresponding direction and / or a sub scanning corresponding direction is set so as to reduce shading well.