JP2009168923A - Optical scanning device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device in which depth tolerance is increased while keeping a beam spot diameter small as well as changes in an imaging position caused by environmental changes are effectively suppressed. <P>SOLUTION: The optical scanning device includes a light source, an aperture, a phase optical element, a deflecting means and a scanning lens. In the device, one optical plane of the phase optical element is divided into a plurality of regions An (n=1, 2, ...) to form the optical plane as a discontinuous plane figure, and a phase distribution figure BP of a structure pattern B different from the figure of the regions An (n=1, 2, ...) is provided, so that a function of correcting a positional shift of an imaging plane due to environmental changes is imparted to the discontinuous face figure comprising the plurality of regions An and that a function of increasing the depth of focus of a light spot is imparted to the structural pattern B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus. The optical scanning device of the present invention can be used in digital copying machines, laser printers, laser facsimiles, MFPs (multifunction printers), etc., and the image forming apparatus can be implemented as these devices.

In recent years, the required level of image quality of an output image of an “image forming apparatus such as an MFP” that forms an image by optical scanning has increased, and there has been a strong demand for reducing and stabilizing the beam spot diameter in optical scanning. “Stabilization of the beam spot diameter” can be achieved by increasing the beam depth margin (defocus distance in the optical axis direction that is equal to or less than the allowable beam spot diameter), but the depth margin: d and the beam spot diameter: W As is well known, between the wavelength used in optical scanning: λ,
d∝w ² / λ
Since the increase in the depth margin results in an increase in the beam spot diameter, it is difficult to achieve both “reduction and stabilization” of the beam spot diameter.
As a method of “expanding the depth margin” while keeping the beam spot diameter small, a method using a Bessel beam is conceivable. Although the Bessel beam is known from Patent Document 1, etc., the side lobe light intensity is very strong and the intensity of the high-order side lobe light is also strong. From the viewpoint of speeding up image formation that has been recently requested, there is no problem.

  Further, there is a problem that image formation by optical scanning is easily affected by “environmental fluctuation”. When the temperature and humidity, which are the environmental conditions in which optical scanning is performed, change, the wavelength of the laser light source used as the light source changes, or the optical characteristics change due to thermal deformation of the lens. The image plane is displaced. It has been proposed to reduce the displacement of the image plane due to environmental fluctuations using a diffractive lens (Patent Document 2, etc.).

Japanese Patent No. 3507244 JP-A-2005-258392 JP 2006-235069 A

  In view of the above, it is an object of the present invention to increase the depth margin while keeping the beam spot diameter small, and at the same time, to effectively suppress fluctuations in the image plane position due to environmental changes. .

  The optical scanning device according to the present invention is “a light source, an aperture that transmits only a part of the light beam from the light source, a phase-type optical element, a deflection unit that deflects and scans the light beam, and a beam scanned by the deflection unit. An optical scanning device having a scanning lens that forms an image of a scanning beam on a surface to be scanned.

  The optical scanning device according to claim 1 has the following characteristics.

  That is, one optical surface of the phase-type optical element is divided into a plurality of regions: An (n = 1, 2,...) So that the optical surface has a discontinuous surface shape. The phase difference between them is set to be “an integral multiple of approximately 2π with respect to the used wavelength”, and the structure pattern: B having a different shape from the region: An (n = 1, 2,...) Is formed on the optical surface. The structure of the structure pattern: B is set so that the phase difference between the structure pattern: B and its peripheral portion is “different from 2π with respect to the wavelength used”. Then, a discontinuous surface shape by a plurality of regions: An (n = 1, 2,...) Is provided with a “function for correcting the positional deviation of the imaging surface due to environmental fluctuations”, and the structure pattern: B It has a function to expand the depth of focus.

  2. The optical scanning device according to claim 1, wherein the discontinuous surface shape of the plurality of regions of the phase-type optical element: An (n = 1, 2,...) “Does not have a function of converging or diverging a light beam having a working wavelength”. (Claim 2).

  3. The “plurality of regions in the discontinuous surface shape: Discontinuous portions of An (n = 1, 2,...)” Of the phase optical element in the optical scanning device according to claim 1 or 2 is linear, circular, or elliptical. In shape, the structure pattern B can be a “two-dimensional pattern”. In this case, the two-dimensional pattern of the structural pattern B in the phase-type optical element “has line symmetry in the main scanning direction and sub-scanning direction and does not have rotational symmetry with respect to a rotation angle of 90 degrees”. Preferred (claim 4). “Rotation angle: not having rotational symmetry with respect to 90 degrees” means that when a two-dimensional pattern is rotated 90 degrees in the pattern plane, it is not the same as the pattern shape before the rotation.

  The two-dimensional pattern B of the phase type optical element in the optical scanning device according to claim 4 can be “including at least part of an elliptical ring shape, and the width of the elliptical ring shape is not uniform” (claimed) Item 5).

  6. The phase-type optical element of the optical scanning device according to claim 1, wherein a plurality of regions: a discontinuous surface shape by An (n = 1, 2,...) And a structural pattern: B are formed. The surface opposite to the “surface” can form a “refractive lens surface”.

  The optical scanning device according to any one of claims 1 to 6, wherein the "aperture that allows passage of only a part of the light beam from the light source" may have a "rectangular shape with four corners chamfered". (Aspect 7) In the optical scanning device according to any one of claims 1 to 7, the "aperture that allows only a part of the light beam from the light source to pass" is disposed in close proximity to the phase optical element. Alternatively, it can be in close contact with or integrated with the phase type optical element. In this case, the “light source can be a multi-beam light source” (claim 9).

  The discontinuous surface shape by a plurality of regions: An (n = 1, 2,...) In the phase-type optical element in the optical scanning device according to any one of claims 1 to 9 is cut to form a structural pattern: B Is preferably formed by etching.

  The image forming apparatus of the present invention is an "image forming apparatus of a type that forms an electrostatic latent image by performing image writing by optical scanning on a photoconductive photosensitive member", and image writing by optical scanning is performed. It is performed by the optical scanning device according to any one of 10 (claim 11).

  12. The image forming apparatus according to claim 11, wherein toner images are formed by performing image writing of different color components on a plurality of photoconductive photoconductors and visualizing electrostatic latent images formed on the photoconductors with different color toners. The toner images of different colors are superimposed on the same recording medium to form a color or multi-color image ”.

  The optical scanning of the surface to be scanned by the optical scanning device may be a “single beam system” or a “multibeam system”.

A little supplementary explanation.
First, the “function for correcting the positional deviation of the imaging plane due to environmental fluctuations” given to the discontinuous surface shape by a plurality of regions: An (n = 1, 2,...) Will be briefly described.
For the sake of concreteness, it is assumed that the phase type optical element is disposed between the light source and the light deflecting means, and the light beam from the light source is collimated and enters the phase type optical element as a parallel light beam. The element is assumed to be light transmissive.
At this time, when the parallel light beam passes through the phase type optical element, it is divided into a plurality of light beam portions according to the region: An, but the phase difference between the regions is “an integral multiple of approximately 2π with respect to the used wavelength”. The phases of the divided light beams are matched, and the transmitted light beam as a whole maintains a plane wave, that is, a parallel light beam.

  The emission wavelength of a semiconductor laser or surface-emitting laser generally used as a light source has a general property that “the emission wavelength shifts to the longer wavelength side” as the temperature rises. On the other hand, the scanning lens of an optical scanning device generally has a positive refractive power in order to focus the deflected light beam on the surface to be scanned. Generally, the positive lens appears to have a weak positive power, and the negative lens has a negative power to appear weak.

  For the sake of concreteness, considering the case where the scanning lens is a positive lens and the positive power becomes weaker as the temperature rises, as described above, phase-type optics in which the transmitted light beam is a parallel light beam at the wavelength used. In the case of an element, when the wavelength increases due to a temperature rise, the phases of the light beam portions transmitted through each region: An are shifted from each other. At this time, by adjusting the shape of the discontinuous surface by the region: An, the light beam having an increased wavelength can be made to be a “convergent light beam” after passing through the phase optical element.

  Thus, when the light beam that has become a “convergent light beam” enters the “scanning lens with a weak positive power”, the decrease in positive power in the scanning lens is reduced by the “convergence property of the light beam”. Then, by adjusting the shape of the discontinuous surface, the change to the convergence of the light beam can cancel out the “decrease in positive power in the scanning lens”. Even when the lens affected by the environmental fluctuation is a negative lens, the “reduction in negative power in the scanning lens” can be canceled by adjusting the shape of the discontinuous surface.

In this way, a “function for correcting the positional deviation of the imaging plane due to environmental fluctuations” can be given to the discontinuous surface shape by a plurality of regions: An (n = 1, 2,...). Although the correction of the power fluctuation of the scanning lens has been described above, generally, the fluctuation of the imaging plane position caused by the power fluctuation of the lens arranged on the optical path from the light source to the scanned surface is referred to as the discontinuous surface. It can be corrected by adjusting the shape.
On the other hand, the structure pattern: B “expands the depth of focus of the light spot as in the example described later” by “setting the structure so that the phase difference with the peripheral portion is different from 2π with respect to the wavelength used”. "Function" can be provided.

  The discontinuous surface shape or structure pattern B gives a two-dimensional phase distribution to the incident beam. This phase distribution can be realized by, for example, “forming a refractive index distribution or a height distribution on a transparent substrate such as glass or resin”. It is often realized with. In the following, the refractive index distribution and the height distribution given to the discontinuous surface shape and the structural pattern B in order to give a desired phase distribution to the light beam will be referred to as “phase distribution in the phase type optical element”.

The inventor has found the following method as “a method capable of expanding the depth margin without increasing the beam spot diameter”.
That is, in this method, the peak intensity of the side lobe light (the side lobe light just outside the main lobe light) in the beam profile of the beam spot at the image plane position of the scanning lens is set so as not to cause a problem with optical scanning. In order to realize this, in the present invention, the phase distribution of the phase pattern optical element B and its peripheral portion is changed to “the sidelobe light so as not to cause a problem in optical scanning”. It is designed to increase the peak intensity.

When phase adjustment is performed by the phase type optical element, the peak intensity of the main lobe light in the light intensity profile (beam profile) of the beam spot on the imaging surface (designed scanning surface) of the scanning lens: side lobe light with respect to PM Peak intensity: PS ratio: PS / PM is the ratio of the peak intensity of the main lobe light in the light intensity profile at the imaging plane position when phase adjustment is not performed: the peak intensity of the side lobe light: PM1 : For PS1 / PS,
(1) PS / PM> PS1 / PM1
Thus, the phase distribution in the phase type optical element is set.

Further, in the case of performing phase adjustment by the phase type optical element, the peak intensity of the main lobe light in the light intensity profile of the “position on the optical axis other than the imaging plane” of the scanning lens: the peak intensity of the side lobe light with respect to PM2: PS2 When the ratio is PS2 / PM2, the peak intensity of the main lobe light in the light intensity profile at the position when phase adjustment is not performed: the peak intensity of the side lobe light with respect to PMA: the ratio of PSA is PSA / PMA,
(2) PS2 / PM2 <PSA / PMA
Is preferably set so that the phase distribution in the phase-type optical element is satisfied.

Alternatively, the peak intensity of the main lobe light in the “light intensity profile at the position on the optical axis of the scanning lens at the image plane position” when phase adjustment is performed: “light intensity at a position other than the image plane at PM3” Peak intensity of the main lobe light in the “profile”: PM4 ratio: PM4 / PM3 does not perform phase adjustment by the phase optical element, and the peak intensity of the main lobe light in the “light intensity profile at the imaging plane position”: With respect to PM5, the peak intensity of the main lobe light in the “light intensity profile at a position other than the imaging plane”: PM6 ratio: PM6 / PM5,
(3) PM4 / PM3> PM6 / PM5
It is good to be.

  In general, the peak intensity of the light intensity profile of the beam spot at “a position deviating from the imaging plane position” is smaller than the peak intensity at the imaging plane position. As described above, if the amount of decrease in the peak intensity at a position deviating from the image plane position is suppressed, the image forming apparatus can also remove the photoconductor even when the “photographer installation position varies” over time. The amount of light energy to be exposed can be reduced, and the “change in the size of the writing dots” accompanying the fluctuation in the exposure energy can be kept small, which can contribute to the improvement of the image quality of the output image.

  Satisfying the condition (1) is a necessary condition for causing an increase in the depth margin, and the phase distribution in the phase optical element is set so as to satisfy the condition (1).

  The larger the amount of increase in the peak intensity of the sidelobe light, the “the amount of increase in the depth margin increases”. However, if the peak intensity of the sidelobe light is increased too much, It induces the phenomenon of “Chile” and soiling. In addition, the amount of decrease in the main lobe light intensity becomes too large, which may be disadvantageous for speeding up the optical scanning.

  Therefore, the peak intensity of the side lobe light is set to 13.5% or less, preferably 10% or less of the peak intensity of the main lobe light.

  As described above, according to the present invention, a novel optical scanning device and image forming apparatus can be realized. The optical scanning device according to the present invention increases the depth margin while keeping the beam spot diameter of the optical scanning small, and at the same time, can effectively suppress the fluctuation of the imaging position due to the environmental change, so that it is not influenced by the environment. Stable optical scanning can be realized. Therefore, the image forming apparatus using the optical scanning device of the present invention can realize stable image formation regardless of environmental changes.

FIG. 1 shows an example of the optical arrangement of the optical scanning device.
FIG. 1 shows an optical system constituting an optical path from the light source 1 to the surface to be scanned 11 virtually developed in one plane.
As shown in FIG. 1, the light beam emitted from the light source 1 is collimated by the coupling lens 3, passes through the optical member 12, and tends to converge in the sub-scanning direction (direction orthogonal to the drawing) by the cylindrical lens 5. Is formed as a “line image long in the main scanning direction” in the vicinity of the deflection reflection surface of the polygon mirror 7 which is the deflection means. In this embodiment, the polygon mirror 7 has four deflection reflection surfaces.

The light beam reflected by the deflection reflection surface of the polygon mirror 7 is condensed as a beam spot on the surface 11 to be scanned by the action of the lenses 8 and 10 constituting the “scanning lens”. The lenses 8 and 10 can be formed of glass or resin.
When the polygon mirror 7 rotates at a constant speed, the light beam reflected by the deflecting reflecting surface is deflected at a uniform angular velocity, and the beam spot optically scans the scanned surface 11.
The optical member 12 is “aperture and phase optical element that are in close proximity to each other”, and the aperture shape blocks the light beam area around the light beam and shapes the beam, and the phase of the wave front is adjusted by the phase optical element. Increase the depth margin to compensate for the effects of environmental fluctuations.

The scanning lens constituted by the lenses 8 and 10 is a so-called “fθ lens” in terms of function, and has a function of making the displacement of the beam spot of the light beam deflected at a constant angular velocity on the scanned surface 11 constant. Have.
The scanning lens by the lenses 8 and 10 also has a position of the deflecting reflection surface of the polygon mirror 7 and the position of the surface 11 to be scanned “in a conjugate relationship with respect to the sub-scanning direction”. Since the “long line image” becomes an object point of the scanning lens, the “face tilt” of the polygon mirror 7 is corrected. In the example being described, the two lenses 8 and 10 constituting the scanning lens are both made of resin.

The actual surface 11 to be scanned in FIG. 1 is a “photoconductive surface of a photoconductive photoconductor”.
The optical scanning device having the optical arrangement shown in FIG. 1 has a configuration that has been widely known so far, except for the phase-type optical element portion of the optical member 12. The optical scanning device having the configuration shown in FIG. 1 can be combined as shown in FIG. 2 to constitute a “tandem optical scanning device”. FIG. 2 shows a state in which the optical system portion of the tandem type optical scanning device is viewed from the sub-scanning direction, that is, the rotational axis direction of the polygon mirror 7 which is a deflecting means. For the sake of simplicity of illustration, the illustration of the mirror for bending the optical path on the optical path from the polygon mirror 7 to each scanned surface that is the optical scanning position is omitted, and the optical path is drawn on a plane.

  In this optical scanning device, the four scanned surfaces 11Y, 11M, 11C, and 11K are optically scanned with light beams, respectively. The substance of the four scanned surfaces 11Y, 11M, 11C, and 11K is “the photosensitive surface of the photoconductive photosensitive drum”, and the electrostatic latent images formed on the four photosensitive drums are magenta, yellow, Visualization is individually performed with cyan and black toners, and the obtained four color toner images are superimposed to form a color image. Accordingly, in the following description, a common reference numeral is assigned to the surface to be scanned and the photosensitive drum that forms the surface.

  In FIG. 2, reference numerals 1Y, 1M, 1C, and 1K denote “light sources”. The light sources 1Y and 1M are arranged so as to overlap in the sub-scanning direction that is a direction orthogonal to the drawing. The light source of the light source 1M is intensity-modulated by “image signal corresponding to magenta image”, and the light source of the light source 1Y is intensity-modulated by “image signal corresponding to yellow image”.

  Similarly, the light sources 1C and 1K are also arranged so as to overlap in the sub-scanning direction, the light source of the light source 1C is intensity-modulated by “image signal corresponding to a cyan image”, and the light source of the light source 1K “corresponds to a black image”. The intensity is modulated by the “image signal”.

  The light beams emitted from each of the light sources 1Y and 1M are converted into parallel light beams by the coupling lenses 3Y and 3M (which are arranged in the sub-scanning direction so that the light beams from the respective light sources are incident). After passing through 12M (arranged so as to overlap each other in the sub-scanning direction, light shielding (beam shaping) of the peripheral luminous flux region of each light beam and phase adjustment for increasing the depth margin) are performed, and then arrayed in the sub-scanning direction The cylinder lenses 5Y and 5M (disposed so as to overlap in the sub-scanning direction) are condensed in the sub-scanning direction and enter the polygon mirror 7.

  A plurality of “line images that are long in the main scanning direction” by the cylinder lenses 5Y and 5M are imaged in the vicinity of the deflecting reflection surface of the polygon mirror 7, and the deflected light beams are transmitted through the lenses 8Y, 8M, 10Y, and 10M, respectively. The beam spots are formed on the scanned surfaces 11Y and 11M by the action of these lenses, and the scanned surfaces are optically scanned.

  Similarly, the light beams emitted from the multi-beam light sources 1C and 1K are converted into parallel light beams by the coupling lenses 3C and 3K, and after passing through the optical members 12C and 12K, the cylinder lenses 5C and 5K arranged in the sub-scanning direction. Are condensed in the sub-scanning direction, incident on the polygon mirror 7, deflected, and transmitted through the lenses 8C, 8K, 10C, and 10K, respectively, and a beam spot is formed on the scanned surfaces 11C and 11K by the action of these lenses. These scanned surfaces are optically scanned. The lens 8Y and the lens 10Y, the lens 8M and the lens 10M, the lens 8C and the lens 10C, and the lens 8K and the lens 10K respectively constitute a scanning lens.

FIG. 3 is a diagram showing a configuration of an image forming apparatus using the optical scanning device shown in FIG. In FIG. 3, the portion indicated by reference numeral 20 is the portion of the “optical scanning device” described with reference to FIG.
The polygon mirror 7 has four deflecting reflecting surfaces, and has a “two-stage configuration” as shown in FIG. 3. One of the light beams deflected in the upper stage is bent by the optical path bending mirrors mM1, mM2, and mM3. The light path is guided to the photosensitive drum 11M by the optical path, and the other light beam is guided to the photosensitive drum 11C by the optical path bent by the optical path bending mirrors mC1, mC2, and mC3.

  Further, one of the light beams deflected on the lower side of the polygon mirror 7 is guided to the photosensitive drum 11Y by the optical path bent by the optical path folding mirror mY, and the other light beam is bent by the optical path folding mirror mK. The light is guided to the photosensitive drum 11K through the optical path.

  Accordingly, the four photosensitive drums 11Y, 11M, 11C, and 11K are optically scanned by the light beams from the four light sources 1Y, 1M, 1C, and 1K. Each of the photosensitive drums 11Y to 11K is rotated at a constant speed in the clockwise direction, and is uniformly charged by the charging rollers TY, TM, TC, and TK that form a charging unit, and is subjected to the corresponding optical scanning, thereby yellow, magenta, cyan, and black. Each color image is written and a corresponding electrostatic latent image (negative latent image) is formed.

  These electrostatic latent images are reversed and developed by developing devices GY, GM, GC, and GK, respectively, and a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are respectively formed on the photosensitive drums 11Y, 11M, 11C, and 11K. It is formed.

  These color toner images are transferred onto a “transfer sheet” (not shown). That is, the transfer sheet is conveyed by the conveying belt 17, the yellow toner image is transferred from the photosensitive drum 11Y by the transfer device 15Y, and magenta from the photosensitive drums 11M, 11C, and 11K by the transfer devices 15M, 15C, and 15K, respectively. The toner image, cyan toner image, and black toner image are sequentially transferred.

  In this way, a yellow toner image to a black toner image are superimposed on the transfer sheet to compose a color image synthetically. This color image is fixed on the transfer sheet by the fixing device 19. The toner images formed on the respective photosensitive drums may be superimposed on the intermediate transfer belt to form a color image, and the color image may be transferred and fixed on the transfer sheet.

  In FIG. 3, the lenses 8Y and 8M on which the light beam deflected to the right side of the polygon mirror 7 is incident are drawn separately in the figure, but they may be integrated in two stages. In FIG. 3, the same applies to the lenses 8C and 8K on which the light beam deflected to the left side of the polygon mirror 7 enters.

In the embodiment described above, as described with reference to FIG. 1, the optical member 12 is “the aperture and the phase optical element are arranged in close proximity”.
As will be described later, the aperture is used to effectively suppress fluctuations in the beam spot diameter, and performs beam shaping. However, when the aperture is provided, the beam profile of the beam spot is changed to “main” due to the influence of diffraction at the aperture. “Profile with side lobe light around the lobe light”.
On the other hand, if a phase type optical element is used, “diffracting also occurs in the phase type optical element”, the beam profile of the beam spot on the image plane of the light beam is “a combination of diffraction by the aperture and diffraction by the phase type optical element. Formed as ". Therefore, by changing the phase distribution of the phase type optical element, the beam profile of the beam spot can be changed, and this is used to reduce the narrowing of the depth margin while suppressing the increase of the beam spot diameter. Or you can prevent.

  4A to 4D show four specific examples of the structural pattern B of the phase type optical element.

In the example of FIG. 4, the phase distribution of the structural pattern: B (dark portion) in the phase type optical element is “height: h distribution” as illustrated in FIG. 4A, and the height: h Is set to be “a phase other than 2π (rad)” with respect to the used wavelength: λ. In the case of a distribution using only “the two-step heights of 0 and h” as in the illustrated example, it is preferable to set the height: h so as to be “near π (rad)”.
For height: h, wavelength used: λ, material refractive index: n, phase: θ (rad) is
θ = 2π (n−1) h / λ
It is represented by

  In the example of FIG. 4, the phase distribution by the two-stage height distribution is shown, but there is an advantage that the design margin can be widened by using multiple stages or continuous values. In addition, since the beam profile on the imaging surface is preferably “symmetrical with respect to the main scanning direction and the sub-scanning direction”, the phase distribution of the structural pattern B in the phase type optical element is shown in FIGS. As shown in (d), “a height distribution that is line-symmetric with respect to the main scanning and sub-scanning directions through the center of the element” is preferable.

  Structure patterns B shown in FIGS. 4A and 4B are examples in which “two-dimensional free phase distribution” is set in a pixel structure, and FIG. 4A shows “main scanning direction and sub-scanning direction”. (B) has "the same objectivity in the main scanning direction and the sub-scanning direction".

  4C shows an elliptical ring structure, and FIG. 4D shows a “structure in which a part of elliptical shapes (or circular shapes) are combined”, both of which have a phase distribution of the structural pattern B in the phase type optical element. Suitable. Of course, the pattern of the structure pattern B is not limited to that shown in FIG.

  When used in the optical scanning device shown in FIGS. 1 to 3, since the scanning lens has different magnifications in the main scanning direction and the sub-scanning direction, “90” as shown in FIGS. 4A, 4C, and 4D. “Pattern without symmetry with respect to degree rotation” is good. The pattern of the phase distribution of the phase type optical element: B is a two-dimensional free pattern as shown in the example of FIG. 4A, and is a line in each of the main scanning direction and the sub-scanning direction. It is preferable to set a symmetric height distribution and not to have symmetry with respect to a 90 degree rotation.

Hereinafter, the expansion of the depth margin by the “structural pattern in the phase type optical element: phase adjustment by B” will be described.
The simulation results when the structural pattern B of the phase type optical element is designed so as to satisfy the above items are shown below. Hereinafter, a phase-type optical element capable of expanding the depth margin is also referred to as a “depth expanding element”.

The optical system used for the simulation is as shown in FIG.
In FIG. 5, reference numeral 121 denotes an aperture, reference numeral 122 denotes a phase-type optical element, reference numeral L denotes a lens, and reference numeral IS denotes an imaging plane.
The incident beam is a “plane wave of uniform intensity”, shaped into a desired beam cross-sectional shape by the aperture 121, and a desired phase distribution by the phase-type optical element 122 provided in close contact (distance: 0) with the aperture 121. And an image is formed at the position of the image plane IS by an ideal lens (no aberration lens) having a focal length of f. The aperture 121 and the phase type optical element 122 are installed at the front focal position of the lens L. The various parameters of the simulation are as follows.

Aperture: Diameter: 930μm circular shape
Lens focal length: f = 50mm
Wavelength used: 632.8 nm
The incident beam is a “plane wave of uniform intensity”, but the intensity distribution of a semiconductor laser or the like used as a light source in the optical scanning device is a Gaussian distribution. However, the following description also holds when the incident beam is a Gaussian beam. This is because the expansion of the depth margin by the structure pattern B is “controlling the beam profile on the image plane by controlling only the phase distribution”.

  The aperture 121, the phase-type optical element 122, and the lens L are, for example, a simplified model of the optical member 12, the cylindrical lens 5, and the scanning lenses 8, 10 in the optical arrangement of FIG. Although different from the optical system configuration in the apparatus, the actual optical scanning apparatus can also provide the same qualitative effects as shown below.

“When no depth expansion element is provided”
First, FIG. 6A shows a simulation result of the “beam profile at the imaging plane position” when the depth expanding element 122 is not provided in the model of FIG. The peak intensity is normalized to 1. At this time, the peak intensity of the sidelobe light is 0.016 (1.6% of the peak intensity).

FIG. 6B is a “depth curve with the beam spot diameter (unit: μm) as the vertical axis and the defocus (deviation from the lens imaging position, unit: mm) as the horizontal axis”. This is the size of the intensity portion that is “1 / e ² ” with respect to the peak intensity. If the depth allowance is “allowing the increase in beam spot diameter to 105% of the minimum beam spot diameter”, the depth allowance in the case of FIG. 6 is 8.9 mm.

"When a depth expansion element is provided"
Hereinafter, simulation results when five types of depth expanding elements (five types of structural patterns: B) are used are shown in FIGS. In common with FIGS. 7 to 11, (a) shows “structural pattern in depth-enlarging element: B phase distribution”, (b) shows “beam profile at image plane position”, and (c) shows beam spot. A “depth curve” is shown with the diameter on the vertical axis and the defocus on the horizontal axis. All the “beam profiles” “normalize peak intensity to 1”.

  7A to 11A, the structural pattern B is a “dark portion”, and the phase difference between the structural pattern B and the “light color portion” that is the ground portion and the structural pattern B. Is set to “π (light color portion: 0, dark color portion: π)”.

  The “depth expanding elements” shown in FIGS. 7A to 11A are sequentially referred to as depth expanding elements 1 to 5. Each of the depth expanding elements shown in FIGS. 7 to 11A has a phase distribution of the structure pattern: B having a “hollow circular shape”, and each has an outer diameter and an inner diameter as shown in the figure, and a circular phase distribution. The center of is matched with the “center of the aperture”.

  As shown in FIG. 7 to FIG. 11B, the peak of the high-order sidelobe light is low even when the depth expanding elements 1 to 5 are used (strong outside the graphs of FIG. 7 to FIG. 11B). Intense high-order light is not generated.) High-intensity main lobe light is obtained. Further, as is clear from the comparison with FIG. 6A showing the beam profile when the depth expanding element is not used, the use of the depth expanding elements 1 to 5 makes it adjacent to the main lobe light in the beam profile. The peak value of the sidelobe light to be increased.

  Further, by using the depth expanding elements 1 to 5, as apparent from the “depth curve” shown in FIGS. 7 to 11C, the change of the beam spot diameter with respect to the defocus is reduced, and the depth margin is increased. is doing.

"When using a phase-type optical element with a structure pattern without depth expansion"
In the structure pattern shown in FIG. 12, the phase distribution is “hollow circular shape with phase difference: π”, similar to the depth expanding elements 1 to 5, and has the outer and inner diameters shown in the figure, and the center of the circular phase distribution. Is matched with the “center of the aperture”.
However, the beam profile obtained in this case has a small peak value of the sidelobe light adjacent to the main lobe light as shown in FIG. 12B, and as is clear from FIG. Has no function to do.

  FIG. 13 shows a list of the peak intensity, depth margin, and beam spot diameter of the sidelobe light in each case described above.

  The “beam profile” is calculated assuming that the peak intensity is standardized to 1 and the depth margin is “allowing an increase in beam spot diameter to 105% of the minimum beam spot diameter”. In FIG. 13, “no depth expansion element” is the case shown in FIG. 6, and “the depth expansion element not according to the present invention” is “a phase type optical element having a structure pattern without a depth expansion function” shown in FIG. .

  “By providing phase-type optical elements (depth expansion elements 1 to 5) that increase the peak intensity of the sidelobe light, the depth margin is expanded, and the one with the strong peak intensity of the sidelobe light has a greater depth margin. It is understood that the enlargement rate is large.

  In the case of using “a phase type optical element having a structure pattern without a depth expansion function”, it can be seen from FIG. 13 that the depth margin is decreased.

  As described above, when the depth expanding element having the structural pattern B is used, the depth margin of the beam spot diameter in the vicinity of the lens focal point position is expanded, so that a layout such as the addition of a lens such as a relay optical system is not caused. Above all, it is very advantageous. Furthermore, “high light utilization efficiency” can be realized.

  FIG. 14 shows the defocus (mm) on the horizontal axis and the peak intensity of the sidelobe light (main lobe) on the vertical axis when “no depth expansion element is used” and when each of the depth expansion elements 1 to 5 is used. (When the peak intensity of light is normalized to 1), the relationship between the two is shown. When the structure pattern of FIG. 12 is used, the beam profile is not significantly deteriorated except at the focal position, the side lobe light and the main lobe light overlap, and the peak intensity of the side lobe light and the main lobe light cannot be distinguished from each other. .

  Referring to FIG. 14, at the focal position (image plane position, defocus: 0 mm), the peak intensity of the sidelobe light when the depth expanding element is not used is the smallest, but the defocus is larger than 5 to 6 mm. In the defocus region, the peak intensity of the sidelobe light is smaller when the depth expanding element is used.

  Although the “hollow circular (ring-shaped)” phase distribution of the structural pattern B is shown above, it is not limited to this, and as described above, “the side just outside the main lobe light” A structural pattern B having a phase distribution designed to “increase the peak intensity of the lobe light” can be used. For example, the phase distribution as shown in FIG. 4 can be set.

In the above, the simple optical system shown in FIG. 5 has been described, but the above can be applied to an actual optical scanning device. This will be described below.
In a general optical scanning device, the light beam that has passed through the coupling lens becomes substantially parallel light and enters the aperture. The light beam that has passed through the aperture passes through the cylindrical lens and the scanning lens and reaches the surface to be scanned. The cylindrical lens and the scanning lens can be regarded as a single lens in a pseudo manner. However, the power in the main scanning direction and the sub-scanning direction are different, and generally the power in the sub-scanning direction is strong. Therefore, a lens that is regarded as a single pseudo lens is an anamorphic lens.

  In addition, the aperture opening generally has a wide shape in the main scanning direction (many rectangular or elliptical shapes). Accordingly, if the simulation lens shown in FIG. 5 is considered as an anamorphic lens, it corresponds to a general optical scanning device. Although the focal length differs depending on the optical scanning device, the above-described depth expansion does not depend on the focal length.

  The above is the description of the “depth-of-focus function” by the structure pattern B. In the following, the function of “image plane displacement correction due to environmental fluctuations” due to the discontinuous surface shape of a plurality of regions: An (n = 1, 2,...) Will be described.

  A diffractive lens is known as a lens having a function of performing “correction of image plane position displacement due to environmental fluctuations”. FIG. 15 shows an example of a structure of a conventionally known diffractive lens (the upper figure is a view seen from the optical axis direction, and the lower figures are sectional views).

FIG. 15A shows a structure in which the shape of a normal lens is divided into ring zones, and folded so that the height of each ring zone is “h”.
FIG. 15B shows a shape (sawtooth cross section) in which the inclined surface of the annular zone in FIG.

  FIG. 15C is an “approximation of the annular zone of (a) with a shape having a step-like cross section”.

  The individual annular zone portions in these examples are individual regions of a plurality of regions: An (n = 1, 2,...), And the annular zone group has a “discontinuous surface shape” as a whole. The discontinuous surface shape is set so as to have “a function for correcting the positional deviation of the imaging surface due to environmental fluctuations”.

The discontinuous surface shapes in FIGS. 15A to 15C have power at the “use wavelength (design wavelength)” and collect (or diverge) the incident beam.
The example shown in FIG. 16 is a “diffractive lens having no power at the wavelength used”. Each annular zone constituting the plurality of regions: An is a plane perpendicular to the optical axis.

  The height “h” shown in FIGS. 15 and 16 is set to have a phase difference of “integer multiple of 2π” with respect to the used wavelength.

Considering the case where the temperature in the optical scanning device rises, when a semiconductor laser is used as the light source, the light emission wavelength of the light source generally shifts to the longer wavelength side, but the power of the diffractive lens increases in proportion to the wavelength. .
When the temperature rises, a lens having a refractive action (particularly a resin lens) expands, the curvature of the lens surface decreases, and the lens power becomes weak. Therefore, if both the diffractive lens and the refractive lens are provided in one optical system, the power change at the time of temperature change can be canceled by the diffractive lens and the refractive lens, and the power change due to the temperature change can be suppressed. That is, the power change of the diffractive surface in the diffractive lens is opposite to the “direction of power change due to expansion / contraction of the lens due to temperature change”, and the change of the image plane position when the temperature changes can be suppressed.

  FIG. 17 shows three types of discontinuous surface shapes (a plurality of regions: discontinuous surface shapes by An) of the lens surface of the diffractive lens. In (a), the plurality of regions are annular zones divided into “concentric circles”, in (b) the plurality of regions are annular zones divided into “concentric ellipses”, and in (c), the plurality of regions Is a strip-shaped region group divided by a linear dividing line. According to the discontinuous surface shapes of (b) and (c), “anamorphic diffraction power” can be realized.

  In general, since the optical system magnification is different between the main scanning direction and the sub-scanning direction in the optical scanning device, the amount of change in the image plane position caused by the diffraction lens when the temperature changes is different between the main scanning direction and the sub-scanning direction. It is preferable to set to. For this purpose, one diffractive lens surface having an elliptical annular zone as shown in FIG. 17 (b) is used, or a diffractive lens having concentric annular zones as shown in FIG. 17 (a). It is preferable to use a combination of the surface and a diffractive lens surface divided by a linear dividing line as shown in FIG.

  In general, since the magnification in the sub-scanning direction is high and the magnification in the main scanning direction is relatively small in the optical scanning device, a change in the sub-scanning direction is particularly problematic with respect to a change in the imaging plane position when the temperature changes.

  Therefore, the effect can be obtained even with one diffractive lens surface having a concentric ring zone as shown in FIG. 17A or one diffractive lens surface as shown in FIG.

  The principle of changing the power of the diffractive surface with a change in temperature has been described above. This corresponds to generating a spherical wave (divergent or convergent) on the diffractive surface. By applying this, an arbitrary wavefront can be generated when the temperature changes, and for example, a wavefront that cancels various aberrations that occur when the temperature changes can be generated. This can be realized by changing the method of dividing the region: An and changing the width and size of the region: An.

  Above, “the function of expanding the depth margin” by the structure pattern: B and “the function of correcting the influence of environmental variation” by the discontinuous surface shape by the plurality of regions: An are individually described. Since these two functions utilize independent optical phenomena, the two functions can be made to function simultaneously by combining them.

  That is, according to the present invention, as described in claim 1, “one optical surface” of the same phase type optical element is divided into a plurality of regions: An (n = 1, 2,...), And the optical surface is divided. A discontinuous surface shape is set, and the phase difference between the regions in the discontinuous portion of the discontinuous surface shape is set to be an integral multiple of approximately 2π with respect to the used wavelength, and the region: An (n = 1, 2,...) Having a different structure pattern: B, and the structure pattern: B so that the phase difference between this structure pattern: B and its peripheral portion is different from 2π with respect to the wavelength used Is set to a discontinuous surface shape by a plurality of areas: An having “a function of correcting the positional deviation of the imaging surface due to environmental fluctuations”, and a structure pattern: B “function to expand the depth of focus of a light spot ( It has a function to expand the depth margin).

  FIG. 18 shows two examples of “integrating a diffractive lens structure (discontinuous surface shape) and a depth expansion structure (structure pattern: B)” on the same optical surface of a phase optical element. The integration of the diffractive lens structure and the depth expanding structure on the same plane can be realized by “raising or lowering the depth expanding structure portion” with reference to the diffractive lens structure.

In FIGS. 18A and 18B, a hatched pattern (indicated by reference numeral BP) is a portion of the structure pattern B corresponding to the depth-enlarging structure, and the height of the pattern is the height of the diffractive lens structure. It is “lower by h ₂ ” with respect to the area surface An (n = 1, 2,...).

“H” and “h ₂ ” shown in the figure need to be different from each other, and h ₂ is preferably “a phase difference with respect to the used wavelength: a magnitude that gives π”. The enlargement effect can be generated efficiently. In FIGS. 18A and 18B, the diffractive lens structure (area: annulus corresponding to each of An) is both “elliptical”.

  18A shows a structure pattern B having a depth expansion structure: B is “two-dimensional free pattern BP”, and FIG. 18B shows a structure pattern B having a depth expansion structure “width”. Is an elliptical ring-shaped pattern BP that is not uniform. As described above, the depth-enlarging structure is preferably “structure pattern: B having line symmetry in the main scanning direction and sub-scanning direction and not having 90 ° rotational symmetry”.

  Of course, the diffractive lens structure (discontinuous surface shape) and the depth expansion structure (structure pattern: B) are not limited to the example of FIG. 18, and the diffractive lens structure may be concentric or concentric elliptical as shown in FIG. Alternatively, the depth expansion structure may be a variety of structures as shown in FIG. 4 or a hollow circular shape (ring shape) described above with reference to FIGS. You can also.

  The depth expansion structure (discontinuous surface shape) is most preferably “two-dimensional arbitrary pattern” as in the examples of FIG. 4A and FIG. It becomes difficult, and the durability of the mold may be reduced due to the presence of many fine structures. In consideration of manufacturing stability, the depth expansion structure includes “elliptical ring shape as shown in FIGS. 4C and 4D and FIG. It is better to use “pattern”.

  Also, in order to effectively generate the depth expansion function using the elliptical ring shape, the width of the elliptical ring shape is not constant, and the width in the main scanning direction is made larger than the width in the sub-scanning direction (for example, , A pattern as shown in FIG.

  As described in claim 1, the optical scanning device of the present invention has “aperture that allows passage of only a part of the light beam from the light source” as a constituent feature.

  Semiconductor lasers such as edge-emitting lasers and surface-emitting lasers are generally used as light sources in optical scanning devices, but these have “divergence of divergence angle” between individuals, so the light source of the optical scanning device is used as it is. As a result, a large variation in the “beam spot diameter on the photoconductor” occurs between the optical scanning devices. The function of the aperture is “to make the width of the beam incident on the scanning lens constant, and stabilize the change of the beam spot diameter at the imaging plane position (photoreceptor surface) regardless of the divergence angle variation among the individual semiconductor lasers. "There is.

  In general, in an optical scanning device, in order to perform “surface tilt correction” in the sub-scanning direction, the magnification is different between the main scanning direction and the sub-scanning direction, and the beam spot diameter on the photosensitive member is also different from that in the main scanning direction. It depends on the direction. The scanning lens is an anamorphic optical system having different surface shapes in the main scanning direction and the sub-scanning direction, and the aperture is generally “long in the main scanning direction”.

  As described in claim 1, by using a combination of a structural pattern having a depth expansion function: B and a discontinuous surface shape (a diffractive lens surface shape), an effect of suppressing an increase in depth margin and an image plane position shift at the time of environmental change Can be obtained simultaneously, and the beam spot diameter on the photoreceptor can be stabilized.

As described above, since the “function to correct the imaging plane position fluctuation due to the environmental fluctuation” due to the discontinuous surface shape and the depth margin enlargement function by the structure pattern B are used, the optical principle is independent. It is also possible to provide them separately in the optical system. For example, “a surface having a diffractive lens surface (a plurality of regions: discontinuous surfaces by An) on one surface of a phase-type optical element and a structural pattern: B on the other surface. It is good also as.
However, in this case, it is necessary to align the diffractive lens surface and the structure pattern B with high precision, and the difficulty in element manufacture increases, and the cost of the element increases, or priority is given to cost reduction. If the alignment system is sacrificed, the quality of the device will deteriorate. In addition, considering that the phase type optical element is “made with resin using a mold”, it is difficult to manufacture a mold having a complicated surface shape and its life is short. It is easy to invite and is not preferable.

  Furthermore, the phase-type optical element also provided with a “normal refracting surface” can realize cost reduction and improved light utilization efficiency by reducing the number of components, but the surface having the above-described discontinuous surface and structural pattern: B In order to provide a function of a refracting surface to an optical element that is divided into one surface, it is necessary to further integrate a refracting surface on one of the surfaces having a discontinuous surface shape or a structural pattern: B. The difficulty level will increase further.

  Therefore, as described in claim 1, it is preferable to provide a plurality of regions: a discontinuous surface by An and a structural pattern: B on one optical surface of the phase-type optical element. In addition to minimizing the number of points, cost reduction and high light utilization efficiency can be achieved, and the number of diffraction surfaces can be reduced to reduce the difficulty of element fabrication. In this case, the service life of the mold can be increased, and the manufacturing quality can be stabilized.

  When a discontinuous surface shape and a structure pattern: B are provided on one surface of an optical element, a mold is formed so that the discontinuous surface shape of the annular structure and the structure of the structure pattern: B have a “similar relationship”. Although the ring shape is determined by “magnification in the main scanning direction and the sub-scanning direction”, the shape of the phase distribution of the structure pattern B is greatly affected by the shape of the aperture. It is difficult to make the structure of "similar". In order to achieve both suppression of the image plane position change and expansion of the depth margin, it is preferable to make the discontinuous surface shape and the structure pattern B different.

  The phase type optical element is preferably provided “between the light source and the deflecting means”, and can be provided, for example, between the coupling lens and the cylindrical lens. If a discontinuous surface shape having power is used, a coupling lens or a cylindrical lens can be substituted.

  Discontinuous surface / structure pattern of phase type optical element: By providing a refractive lens surface on the surface opposite to the surface provided with B, the refractive lens surface can be used in place of a “coupling lens or cylindrical lens”. The score can be reduced.

  When used in place of the coupling lens, the refractive lens surface is preferably a rotationally symmetric aspheric surface, and the discontinuous surface shape is preferably formed by concentric annular zones. By providing the cylindrical lens with a discontinuous surface divided by linear dividing lines as shown in FIG. 17C, the temperature in the optical scanning device changes in the main scanning direction and the sub-scanning direction. The image plane position change can be suppressed.

  When used in place of a cylindrical lens, the refractive lens surface is preferably a “spherical or aspherical surface having a curvature only in the sub-scanning direction”, and the discontinuous surface shape is a straight line as shown in FIG. It is good to make it the shape divided | segmented by the shape-like division line. Further, the coupling lens may be provided with a discontinuous surface shape by concentric annular zones. Further, when the discontinuous surface shape of the cylindrical lens is formed by a concentric elliptical ring zone, the same function can be realized even if the coupling lens does not have the discontinuous surface shape.

  As described above, the optical scanning device of the present invention can be of a “single beam scanning system” or a “multibeam scanning system”. However, when the multibeam scanning system is used, the light source is a multibeam light source. In some cases, the “difference in the incident position on the element” between the multiple beams is small at the position of the coupling lens, but the “difference in the incident position” between the multiple beams at the position of the cylindrical lens is large, including changes over time. There is a tendency. Therefore, the phase-type optical element is “substituting for a coupling lens” rather than replacing a cylindrical lens with “difference in performance (effect of suppressing variation in image plane position, depth margin expansion effect) between multiple beams”. Is more preferable because

  As a manufacturing method of a phase type optical element in which a discontinuous surface shape and a structural pattern: B are provided on the same optical surface, the discontinuous surface shape is produced by “cutting using a cutting tool”, and the structural pattern: B is dry-etched. Further, it is preferable to fabricate by etching such as wet etching. By using such a method, a mold is first prepared, and then a phase-type optical element is preferably formed from a resin by imprinting or injection molding. Specifically, for example, the following is preferable.

(1) A bite or a mold is rotated (concentric or elliptical) to cut a ring zone structure having a discontinuous surface shape.
(2) Apply a resist.
(3) The structure pattern: B phase distribution shape is drawn by an electron beam or a light beam, or the structure pattern: B phase distribution shape is exposed and developed using a mask.
(4) Evaporate a material with a slow etching rate such as chromium (if necessary) and lift off.
(5) Perform dry etching.

If all are to be performed by cutting, the structure pattern: B spans a ring zone in a plurality of discontinuous surface shapes, which makes machining extremely difficult.
In addition, the number of steps (region: number of An) of the discontinuous surface shape without power is as large as several tens, and the effect of alignment errors during mask exposure and electron / light beam exposure is likely to be produced by etching. Is likely to occur, and it becomes difficult to obtain high diffraction efficiency. Even in the case of a discontinuous surface shape with power, if an attempt is made to obtain high diffraction efficiency, a structure of 8 to 16 steps is required, and 4 to 5 masks are required in combination with the structure pattern: B, resulting in an alignment error. It is difficult to “obtain high diffraction efficiency” due to the influence of the above.

  Therefore, by using cutting and etching together, a mold can be manufactured with high accuracy, and a phase-type optical element having high diffraction efficiency can be manufactured while suppressing generation of wavefront aberration. Thus, a phase type optical element is realizable at low cost by producing a phase type optical element with resin or glass using a type | mold.

  As mentioned above, when machining discontinuous surface shapes by cutting, the type without power is easier to machine, can achieve high-precision machining, and is a phase type that is stable with high accuracy and high diffraction efficiency. An optical element can be manufactured. In addition, it can also be set as a grinding process instead of said cutting process.

  Further, when processing the “surface that is not flat in the height direction” when processing the structural pattern B, “swell” occurs on the processed surface, which may increase the beam spot diameter. Therefore, by processing all flat surfaces (there may be a step in the region to be processed), highly accurate processing can be realized, and the occurrence of wavefront aberration can be suppressed to a small level.

In the present invention, the depth margin is increased by “increasing the peak intensity of the sidelobe light in the vicinity of the position of the image plane of the scanning lens”.
Since sidelobe light is also noise light, the output image may be adversely affected if the “generation” is not properly designed. Sidelobe light in the case where an aperture having a “rectangular opening” is provided is generated in a localized manner in the main scanning direction and the sub-scanning direction, and may adversely affect the output image.

  In consideration of this point, the shape of the aperture in the aperture is, as shown in FIG. 19, “a shape in which four corners are chamfered with respect to the rectangular shape”, that is, an aperture shape that shields the four corners in the light beam cross section. Good. By adopting such an aperture shape, it is possible to avoid that “side lobe light is localized in the main scanning direction and sub-scanning direction” and to surround the main lobe light, and to generate an output image. Adverse effects can be avoided.

  19A is an opening diameter shape with “four corners chamfered with a straight line”, FIG. 19B is an opening diameter shape with “four corners chamfered with an elliptical arc”, and FIG. 19C is an “oval shape”. These are all examples of an embodiment of the invention of claim 7. Further, the total sum of the areas of the four corners to be chamfered is desirably 10% or more of the area of the rectangular opening.

  If the phase type optical element and the aperture are separated from each other, the center position of the structural pattern B and the aperture opening is shifted due to variations in the installation and changes over time, the beam profile on the photoconductor is deteriorated, and the beam spot There is a risk of increasing the diameter. In order to avoid this, the phase optical element and the aperture member may be “closely or in close proximity” or integrated. The most preferable is to “integrate the phase type optical element and the aperture”, and to form a discontinuous surface shape / structure pattern of the phase type optical element: a light shielding region around the surface on which the B is formed or the opposite surface. It is good to form.

  Further, when the light source is a multi-beam light source, for example, when the coupling lens is a phase type optical element, if the aperture member is placed after the phase type optical element, the structure pattern: B and the center of the aperture opening Misalignment is likely to occur.

  FIG. 20 shows this state. A plurality of light beams transmitted through a coupling lens CP having a refracting surface and a discontinuous surface shape / structural pattern: B (“diffractive structure surface” in the figure) are converted into parallel light beams and propagate with an angle to each other. The angle between the light beams differs between the light beams. A beam incident on the aperture AP at a certain angle cannot match the center of the discontinuous surface shape of the phase-type optical element and the center of the aperture with respect to all the beams when viewed from the beam. The further the distance from the mold optical element, the larger the center deviation. Therefore, when the light source is a multi-beam light source, the phase type optical element and the aperture AP are preferably brought into close contact with each other or in close proximity to each other or integrated.

  As the multi-beam light source, for example, a laser diode array in which edge emitting lasers are arranged one-dimensionally or a surface emitting laser array in which surface emitting lasers are arranged two-dimensionally can be used.

It is a figure for demonstrating one example of the optical arrangement | positioning of an optical scanning device. It is a figure for demonstrating an example of the optical arrangement | positioning of a tandem-type optical scanning device. It is a figure for demonstrating an example of an image forming apparatus. It is a figure which shows four examples of the structural pattern: B of a phase type optical element. It is a figure for demonstrating the optical system used for the simulation of expansion of a depth margin. It is a figure which shows a beam profile and a depth curve when not performing phase adjustment by a phase type optical element. It is a figure for demonstrating one example of structure pattern: B. It is a figure for demonstrating one example of structure pattern: B. It is a figure for demonstrating one example of structure pattern: B. It is a figure for demonstrating one example of structure pattern: B. It is a figure for demonstrating one example of structure pattern: B. It is a figure which shows an example of the phase shape which does not have a function which expands a depth margin. It is a table | surface of the peak intensity of a side lobe light, a depth margin, and a beam spot diameter. It is a figure which shows the relationship between the defocus and the peak intensity of sidelobe light about each when not using a depth expansion element and when using the depth expansion elements 1-5. It is a figure which shows one example of the structure of the diffraction lens known conventionally. It is a figure which shows the example of the diffractive lens which does not have power in a reference wavelength. It is a figure which shows three types of discontinuous surface shapes of the lens surface of a diffraction lens. It is a figure which shows two examples which integrated discontinuous surface shape and structural pattern: B on the same optical surface of a phase type optical element. It is a figure which shows the example of the opening shape of an aperture. It is a figure for demonstrating the characterizing part of invention of Claim 8.

Explanation of symbols

1 Light source
3 Coupling lens
12 Optical elements (Aperture and phase type optical elements)
5 Cylindrical lens
7 Deflection means
8, 10 Lens constituting the scanning lens
11 Scanned surface

Claims (12)

A light source, an aperture that allows only a part of the light beam from the light source to pass through, a phase optical element, a deflecting unit that deflects and scans the light beam, and a scanning beam scanned by the deflecting unit is connected to the surface to be scanned. In an optical scanning device having a scanning lens for imaging,
One optical surface of the phase-type optical element is divided into a plurality of regions: An (n = 1, 2,...) To make the optical surface a discontinuous surface shape, and between the regions in the discontinuous portion in the discontinuous surface shape. The phase difference is set to be an integer multiple of approximately 2π with respect to the wavelength used, and the optical surface is provided with a structure pattern: B having a shape different from that of the region: An (n = 1, 2,...) The structure of the structure pattern: B is set so that the phase difference between the structure pattern: B and its peripheral portion is different from 2π with respect to the wavelength used.
The discontinuous surface shape of the plurality of regions: An (n = 1, 2,...) Is provided with a function of correcting the positional deviation of the imaging surface due to environmental fluctuations, and the structure pattern: B has a focus of the light spot. An optical scanning device characterized by having a function of expanding the depth. The optical scanning device according to claim 1,
An optical scanning device characterized in that the discontinuous surface shape by a plurality of regions of the phase-type optical element: An (n = 1, 2,...) Does not have a function of converging or diverging a light beam having a working wavelength. The optical scanning device according to claim 1 or 2,
The discontinuous portions of the plurality of regions: An (n = 1, 2,...) In the discontinuous surface shape of the phase optical element are linear, circular, or elliptical, and the structural pattern: B is a two-dimensional pattern An optical scanning device characterized by that. The optical scanning device according to claim 3.
A light in which the two-dimensional pattern of the structural pattern B in the phase-type optical element has line symmetry in the main scanning direction and the sub-scanning direction and does not have rotation symmetry with respect to a rotation angle of 90 degrees. Scanning device. The optical scanning device according to claim 4.
Structure pattern: An optical scanning device, wherein the two-dimensional pattern of B includes at least a part of an elliptical ring shape, and the width of the elliptical ring shape is not uniform. In the optical scanning device according to any one of claims 1 to 5,
A refractive lens surface is formed on the surface opposite to the surface on which the discontinuous surface shape and the structural pattern: B are formed by a plurality of regions: An (n = 1, 2,...) Of the phase type optical element. An optical scanning device. The optical scanning device according to any one of claims 1 to 6,
An optical scanning device characterized in that an aperture opening that allows passage of only part of a light beam from a light source has a rectangular shape with four corners chamfered. The optical scanning device according to any one of claims 1 to 7,
An optical scanning device characterized in that an aperture that allows passage of only part of a light beam from a light source is disposed in close proximity to the phase optical element, or is in close contact with or integrated with the phase optical element . The optical scanning device according to claim 8.
An optical scanning device characterized in that the light source is a multi-beam light source. The optical scanning device according to any one of claims 1 to 9,
An optical scanning device characterized in that a discontinuous surface shape by a plurality of regions: An (n = 1, 2,...) Of a phase-type optical element is formed by cutting, and a structural pattern: B is formed by etching. In an image forming apparatus of a method for forming an electrostatic latent image by performing image writing by optical scanning on a photoconductive photosensitive member,
An image forming apparatus, wherein image writing by optical scanning is performed by the optical scanning device according to any one of claims 1 to 10. The image forming apparatus according to claim 11.
Images of different color components are written on a plurality of photoconductive photoconductors, and electrostatic latent images formed on the photoconductors are visualized with toners of different colors to form toner images. These different color toner images are the same. An image forming apparatus for forming a color or multicolor image by superimposing on the recording medium.

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