JP5013578B2 - Multi-beam light source unit, optical scanning device, and image forming apparatus - Google Patents

Description

  The present invention relates to a multi-beam light source unit, an optical scanning device, and an image forming apparatus. More specifically, the present invention relates to a multi-beam light source unit that emits a plurality of beams and a surface to be scanned using light from the multi-beam light source unit. The present invention relates to an optical scanning device that scans and an image forming apparatus including the optical scanning device.

  In an image forming apparatus such as a laser printer or a digital copying machine, light from a light source modulated in accordance with image information is condensed on a photoconductor via an optical deflector, a scanning lens, and the like, and the photoconductor is predetermined on the photoconductor. And a latent image (electrostatic latent image) is formed on the photosensitive member. Then, the image information is visualized by attaching toner to the latent image.

  In recent years, it has been desired to improve the printing speed and writing density of image forming apparatuses. One way to achieve these requirements is to increase the deflection speed of the optical deflector of the optical scanning device that forms part of the image forming apparatus. However, this method has problems such as noise and heat accompanying high-speed rotation, and there is a limit to increasing the deflection speed. Therefore, a method of scanning a plurality of light beams at a time using a multi-beam light source unit capable of emitting a plurality of light beams at a time has been devised.

  The multi-beam light source unit can be realized by using a laser array light source (a light source using a laser array having a plurality of light emitting points in one package) that generates a plurality of light beams. However, the laser array light source increases in technical difficulty and becomes very expensive as the number of light emitting points is increased to 4, 8,.

  On the other hand, many proposals have been made for a multi-beam light source unit using a plurality of conventional single beam light sources (light sources using a laser having one light emitting point in one package). Single beam light sources are mass-produced at a low cost. For example, in the case of four single beam light sources and a laser array light source having four light emitting points, the former is superior in cost.

  By the way, in order to construct a multi-beam light source unit using a plurality of single beam light sources, it is necessary to align the light beam from each light source with the optical axis in the same direction, and an optical element for that purpose (so-called beam synthesis element) Have been proposed (see, for example, Patent Document 1 and Patent Document 2). Patent Document 1 discloses a multi-beam scanning device using a half mirror as a beam combining element. Patent Document 2 discloses a multi-light beam scanning optical apparatus using a polarization beam splitter as a beam combining element.

  However, in the apparatuses disclosed in Patent Document 1 and Patent Document 2, the incident directions of the two light beams incident on the half mirror and the polarizing beam splitter are required to be different from each other by 90 degrees. As a result, the design of the multi-beam light source unit is limited, which may adversely affect the miniaturization. In addition, in a polarizing beam splitter, a triangular prism is joined via a thin film, and this thin film exhibits high characteristics when used at the designed wavelength and incident angle, but the characteristics deteriorate when it deviates from the designed value. Has the disadvantage of being large. Further, the polarization beam splitter is an expensive optical element with many manufacturing processes as shown by its shape.

Japanese Patent Laid-Open No. 9-189873 JP-A-9-230260

  The present invention has been made under such circumstances, and a first object of the present invention is to provide a multi-beam light source unit capable of stably emitting a plurality of light beams without causing an increase in size and cost. It is to provide.

  A second object of the present invention is to provide an optical scanning device capable of scanning a surface to be scanned with a plurality of lights with high accuracy without causing an increase in size and cost. .

  A third object of the present invention is to provide an image forming apparatus capable of forming a high-quality image at high speed without causing an increase in size and cost.

The present invention is, to a first aspect, the plurality of light sources and including a first light source and second light source polarization direction for emitting different light beams; a light beam emitted from the first light source A first optical system for shaping; a deflection optical element for deflecting a light beam emitted from the second light source; a second optical system for shaping a light beam deflected by the deflection optical element; The light beam that has passed through the first optical system and the light beam that has passed through the second optical system are incident, and at least a part of the light beam that has passed through the first optical system and the second optical system. A polarization diffractive element that emits at least part of the light beam in the same direction, and the deflection optical element is a diffractive optical element via the second optical system that is emitted from the polarization diffractive element The emission direction of at least part of the light beam A multi-beam light source unit that is independent of the wavelength of the beam.

According to this, without causing large-scale and high cost, it is possible to stably emitting a plurality of light beams.

The present invention is, to a second aspect, the plurality of light sources and including a first light source and second light source whose polarization direction is emitted mutually equal light beam; an optical beam emitted from the first light source A first optical system for shaping; a deflection optical element for deflecting a light beam emitted from the second light source; a second optical system for shaping a light beam deflected by the deflection optical element; The light beam that has passed through the first optical system and the light beam that has passed through the second optical system are incident, and at least a part of the light beam that has passed through the first optical system and the second optical system. A polarization diffraction element that emits at least a part of the light beam in the same direction; on an optical path between the first light source and the polarization diffraction element, or between the second light source and the polarization diffraction element Two light incident on the polarization diffraction element are disposed on the optical path. Beam polarization direction different from each other, and a third optical system for changing the polarization direction of the incident light; wherein the deflecting optical element is a diffractive optical element, said first emitted from the polarization diffraction element The emission direction of at least a part of the light beam via the second optical system is a multi-beam light source unit that does not depend on the wavelength of the light beam .

According to this, without causing large-scale and high cost, it is possible to stably emitting a plurality of light beams.

  According to a third aspect of the present invention, in the optical scanning apparatus that scans a surface to be scanned while deflecting a plurality of light beams including image information by a deflector, the plurality of light beams includes at least one book. An optical scanning device comprising a plurality of light beams emitted from the multi-beam light source unit of the invention.

  According to this, since at least one multi-beam light source unit of the present invention is provided, as a result, the surface to be scanned is scanned with a plurality of lights with high accuracy without causing an increase in size and cost. It becomes possible to do.

  According to a fourth aspect of the present invention, at least one scanning object; at least one optical scanning device of the present invention that scans a plurality of light beams with respect to the at least one scanning object; And a transfer device that transfers an image formed on one scanning object to the transfer object.

  According to this, since at least one optical scanning device of the present invention is provided, as a result, it is possible to form a high-quality image at a high speed without causing an increase in size and cost.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 100 as an image forming apparatus according to an embodiment of the present invention.

  A laser printer 100 shown in FIG. 1 includes an optical scanning device 900, a photosensitive drum 901 as a scanning object, a charging charger 902, a developing roller 903, a toner cartridge 904, a cleaning blade 905, a paper feed tray 906, and a paper feed roller 907. A registration roller pair 908, a transfer charger 911, a fixing roller 909, a paper discharge roller 912, a paper discharge tray 910, and the like.

  The charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are disposed in the vicinity of the surface of the photosensitive drum 901, respectively. Then, with respect to the rotation direction of the photosensitive drum 901, the charging charger 902, the developing roller 903, the transfer charger 911, and the cleaning blade 905 are arranged in this order.

  A photosensitive layer is formed on the surface of the photosensitive drum 901. Here, the photosensitive drum 901 rotates in the clockwise direction (arrow direction) in the plane in FIG.

  The charging charger 902 uniformly charges the surface of the photosensitive drum 901.

  The optical scanning device 900 irradiates the surface of the photosensitive drum 901 charged by the charging charger 902 with light modulated based on image information from a host device (for example, a personal computer). As a result, on the surface of the photosensitive drum 901, the charge is lost only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of the photosensitive drum 901. The latent image formed here moves in the direction of the developing roller 903 as the photosensitive drum 901 rotates. By the way, the longitudinal direction (direction along the rotation axis) of the photosensitive drum 901 is referred to as “main scanning direction”, and the rotational direction of the photosensitive drum 901 is referred to as “sub-scanning direction”. Of the scanning area in the main scanning direction from the scanning start position to the scanning end position on the photosensitive drum 901, an area where a latent image is formed is also referred to as an “effective image forming area”. The configuration of the optical scanning device 900 will be described later.

  The toner cartridge 904 stores toner, and the toner is supplied to the developing roller 903. The amount of toner in the toner cartridge 904 is checked when the power is turned on or when printing is completed. When the remaining amount is low, a message prompting replacement is displayed on a display unit (not shown).

  As the developing roller 903 rotates, the toner supplied from the toner cartridge 904 is charged and thinly and uniformly attached to the surface thereof. Further, the developing roller 903 has an electric field in the opposite direction between a charged portion (a portion not irradiated with light) and an uncharged portion (a portion irradiated with light) in the photosensitive drum 901. A voltage is generated to generate. By this voltage, the toner adhering to the surface of the developing roller 903 adheres only to the portion irradiated with light on the surface of the photosensitive drum 901. That is, the developing roller 903 causes the toner to adhere to the latent image formed on the surface of the photosensitive drum 901 and visualizes the image information. Here, the latent image to which the toner is attached moves in the direction of the transfer charger 911 as the photosensitive drum 901 rotates.

  A recording sheet 913 as a transfer object is stored in the sheet feeding tray 906. A paper feed roller 907 is disposed in the vicinity of the paper feed tray 906, and the paper feed roller 907 takes out the recording paper 913 one by one from the paper feed tray 906 and conveys it to the registration roller pair 908. The registration roller pair 908 is disposed in the vicinity of the transfer roller 911, temporarily holds the recording paper 913 taken out by the paper feed roller 907, and the recording paper 913 is synchronized with the rotation of the photosensitive drum 901. It is sent out toward the gap between 901 and the transfer charger 911.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 911 in order to electrically attract the toner on the surface of the photosensitive drum 901 to the recording paper 913. With this voltage, the latent image on the surface of the photosensitive drum 901 is transferred to the recording paper 913. The recording sheet 913 transferred here is sent to the fixing roller 909.

  In the fixing roller 909, heat and pressure are applied to the recording paper 913, whereby the toner is fixed on the recording paper 913. The recording paper 913 fixed here is sent to the paper discharge tray 910 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 910.

  The cleaning blade 905 removes toner remaining on the surface of the photosensitive drum 901 (residual toner). The removed residual toner is used again. The surface of the photosensitive drum 901 from which the residual toner has been removed returns to the position of the charging charger 902 again.

  Next, the configuration and operation of the optical scanning device 900 will be described with reference to FIG.

  The optical scanning device 900 includes a light source unit LU, a cylindrical lens 14, an optical deflector 15, two scanning imaging lenses 17, a synchronization sensor 18, a reflection mirror 19, and a processing device (not shown in FIG. 2). ing.

  As shown in FIG. 3 as an example, the light source unit LU includes two single beam light sources (LD1, LD2), two lenses (1, 4), a polarizing optical element 2, a diffractive optical element 3, and a λ / 2 plate. 5 etc. Here, as an example, each single beam light source emits TM-polarized light (see FIG. 4).

  The lens 1 shapes the light emitted from the single beam light source LD1 into substantially parallel light. The λ / 2 plate 5 gives an optical phase difference of ½ wavelength to the light from the lens 1. Therefore, the light that has passed through the λ / 2 plate 5 becomes TE polarized light. The diffractive optical element 3 deflects the light emitted from the single beam light source LD2. The lens 2 shapes the light from the diffractive optical element 3 into substantially parallel light. The polarizing optical element 2 aligns the light from the λ / 2 plate 5 and the light from the lens 2 with the optical axes in the same direction. Note that unnecessary light that is not synthesized by the polarization optical element 2 is shielded in at least one of the inside and outside of the optical scanning device so as not to form a light spot on the photosensitive drum 901.

  That is, the light emitted from the single beam light source LD1 and emitted from the lens 1, the λ / 2 plate 5, and the polarization optical element 2 (hereinafter also referred to as “first light beam” for convenience) and the single beam light source LD2. The light (hereinafter, also referred to as “second light beam” for convenience) emitted from the diffractive optical element 3, the lens 4, and the polarizing optical element 2 is emitted from the light source unit LU. The first light beam and the second light beam are emitted in substantially the same direction so as to be condensed at a predetermined interval in the sub scanning direction on the surface of the photosensitive drum 901.

  As an example, the polarizing optical element 2 has a diffraction grating that exhibits structural birefringence, as shown in FIG. Structural birefringence is a periodic structure in which two media having different refractive indices (for example, one is air and the other isotropic medium) is also called SWS (Subwavelength Structure), which is smaller than the wavelength of incident light. Expressed in the diffraction grating. It is also known that structural birefringence occurs in diffraction gratings in which the above two media have a periodic structure that is approximately several times the wavelength of incident light, or a so-called resonance region periodic structure (resonance structure). It has been.

  Therefore, the diffraction grating of the polarizing optical element 2 is a diffraction grating having a sub-wavelength structure or a resonance structure.

  The diffraction efficiency can be controlled by the fill factor f and depth D of the diffraction grating. In practice, the period Λ and the depth D of the diffraction grating are on the order of micrometers with respect to a substrate having a thickness Ds of millimeter order (for example, a glass substrate), and the diffraction grating is exaggerated in FIG. Has been.

The optical characteristics of the polarizing optical element 2 will be described with reference to FIGS. As an example, wavelength λ = 0.633 μm, substrate refractive index N = 1.456, period Λ = 1.5λ, fill factor f = 0.2, depth D = 2.2 μm, incident angle θ of incident light = When the angle of diffraction is 19.5 ° and the diffraction angle when a plane wave is incident is determined based on the lattice equation, θ ₀ = 13.2 ° and θ ₋₁ = −13.2 °. In consideration of refraction at the back surface of the substrate, the emission angle θ ′ of the 0th order transmitted light (0T) = 19.5 °, and the emission angle θ ″ of the −1st order diffracted light (−1T) = − 19.5 ° Next, as a result of calculating the diffraction efficiency of the transmitted light using the Fourier mode method based on the vector diffraction theory, the diffraction when TE polarized light (perpendicular to the paper surface) is incident on the 0th-order transmitted light (0T). The efficiency is 76.1%, the diffraction efficiency when TM polarized light (parallel to the paper surface) is incident is 0.4%, and the extinction ratio is 76.1 / 0.4 = 190. -1T), the diffraction efficiency when TM polarized light is incident is 89.7%, the diffraction efficiency when TE polarized light is incident is 1.2%, and the extinction ratio is 75. The light emitted from each single beam light source has a Gaussian distribution. Since the polarizing optical element 2 in the bundle are arranged, the above diffraction efficiency somewhat different, there is no significant difference so.

  That is, when TE polarized light is incident, the polarization optical element 2 transmits most of it as 0th order light (0T), and when TM polarized light is incident, most of it is −1st order light (−1T). It can be seen that it behaves as a polarization-dependent diffraction element that diffracts as. Accordingly, as shown in FIG. 7, if TE polarized light is incident on the polarizing optical element 2 at an incident angle θa = 19.5 ° and TM polarized light is incident at an incident angle θb = −19.5 °, the TE Both the polarized light and the TM polarized light are emitted from the polarizing optical element 2 at an emission angle θc = 19.5 °.

  By the way, when the wavelength of the light beam emitted from the single beam light source LD2 changes, the diffraction angle in the diffractive optical element 3 changes (see FIG. 8). The change in the diffraction angle in the diffractive optical element 3 causes a change in the emission direction of the second light beam emitted from the light source unit LU. Therefore, in the present embodiment, by appropriately combining the polarizing optical element 2 and the diffractive optical element 3, the emission direction of the second light beam emitted from the light source unit LU is changed to that of the light beam emitted from the single beam light source LD2. It does not depend on the wavelength. This will be described below with reference to FIG. Here, for the sake of clarity, the diffractive optical element 3 is a thin diffraction grating, and the refractive index on the incident side and the outgoing side is 1. Further, the polarizing optical element 2 and the diffractive optical element 3 are arranged so as to be parallel to each other.

  First, consider a case where there is no lens 4 between the polarizing optical element 2 and the diffractive optical element 3. The incident angle of light from the single beam light source LD2 incident on the diffractive optical element 3 is θ2, the outgoing angle is θ2 ′, the diffraction order at the diffractive optical element 3 is m2, the grating period of the diffraction grating is Λ2, and the polarizing optical element 2 The incident angle of light from the incident diffractive optical element 3 is θ1, the exit angle is θ1 ′, the diffraction order at the polarizing optical element 2 is m1, and the grating period of the diffraction grating is Λ1. The lattice equation when the wavelength of light emitted from the single beam light source LD2 is λ is expressed by the following equations (1) and (2).

sinθ1 + m1λ / Λ1 = sinθ1 '(1)
sinθ2 + m2λ / Λ2 = sinθ2 '(2)

  When the wavelength of the light emitted from the light source LD2 changes to λ ″, the emission angle at the diffractive optical element 3 changes to θ2 ″, and the incident angle to the polarizing optical element 2 also changes to θ1 ″. However, in order not to change the exit angle in the polarization optical element 2, m1, m2, Λ1, and Λ2 may be set so that the following lattice equations (3) and (4) are satisfied.

sinθ1 "+ m1λ" / Λ1 = sinθ1 '(3)
sinθ2 + m2λ "/ Λ2 = sinθ2" (4)

  Here, since the polarizing optical element 2 and the diffractive optical element 3 are parallel to each other and θ1 = θ2 ′, the following expression (5) is obtained from the above expressions (1) and (2).

  sinθ2 + λ (m1 / Λ1 + m2 / Λ2) = sinθ1 '(5)

  Similarly, since θ1 ″ = θ2 ″, the following equation (6) is obtained from the above equations (3) and (4).

  sinθ2 + λ "(m1 / Λ1 + m2 / Λ2) = sinθ1 '(6)

  From the above formulas (5) and (6), when the following formula (7) is satisfied, θ1 ′ = θ2 regardless of the wavelength of the light emitted from the light source LD2. That is, even if the wavelength of the light emitted from the light source LD2 changes, the emission direction of the second light beam in the polarizing optical element 2 can be prevented from changing.

  m1 / Λ1 + m2 / Λ2 = 0 (7)

  Next, consider a case where the lens 4 is between the polarizing optical element 2 and the diffractive optical element 3. Considering the chief rays, the above formulas (1) and (2) hold regardless of the focal length of the lens 4. Since the light is in the divergent light, it is not strictly established except for the principal ray, but there is no significant difference because the light direction and aberration are corrected by the lens 4. When the wavelength of the light emitted from the light source LD2 changes from λ to λ ″, the above equation (4) holds as it is. Depending on the lens 4, the incident angle to the polarizing optical element 2 changes from θ1 to ψ. Even so, in order not to change the emission direction of the second light beam in the polarization optical element 2, m1, m2, Λ1,..., So that the above equation (4) and the following lattice equation (8) are satisfied. And Λ2 may be set.

  sinψ + m1λ "/ Λ1 = sinθ1 '(8)

  Here, since the polarizing optical element 2 and the diffractive optical element 3 are parallel to each other and θ1 = θ2 ′, the above equation (5) is obtained, and the above equations (4) and (8) Thus, the following equation (9) is obtained.

  (Sinθ2 "-m2λ" / Λ2) + λ (m1 / Λ1 + m2 / Λ2) = sinψ + m1λ "/ Λ1 (9)

  When the above equation (9) is modified, the following equation (10) is obtained.

  sinθ2 "-sinψ = (λ" -λ) (m1 / Λ1 + m2 / Λ2) (10)

  That is, m1, m2, Λ1, and Λ2 may be set so that the above expression (10) is satisfied. By the way, if m2 / Λ2 is given, θ2 ″ can be obtained with respect to the wavelength variation from λ to λ ″. Since the lens 4 is fixed, ψ with respect to θ2 ″ is obtained. Therefore, m1 / Λ1 is also determined. Here, θ1 = θ2 ′, but the polarizing optical element 2 and the diffractive optical element 3 Even if they are not parallel, it is possible to obtain a condition for not changing the emission direction of the second light beam in the polarizing optical element 2.

  In general, (sinθ2 "-sinψ) does not change proportionally with respect to (λ" -λ), but in the actual wavelength fluctuation (wavelength fluctuation of about several nm) region, (λ "-λ) and ( It can be considered that a proportional relationship is established with sinθ2 "-sinψ).

  Further, if both the polarizing optical element 2 and the diffractive optical element 3 use the first-order diffracted light, it can be transformed to Λ1 = Λ2 + β (β is a constant other than 0), so that the diffraction gratings in the polarizing optical element 2 and the diffractive optical element 3 The periods may be different from each other.

  Here, the case where the polarizing optical element 2 diffracts the TM-polarized light has been described. However, even in the case where the TE-polarized light beam is diffracted, the polarization optical element 2 in the polarizing optical element 2 similarly responds to the wavelength change. It is possible not to change the emission direction of the second light beam.

  Returning to FIG. 2, each light beam emitted from the light source unit LU is incident on the cylindrical lens 14. The cylindrical lens 14 forms an elongated line image in the direction corresponding to the main scanning direction for each light beam in the vicinity of the deflection reflection surface (polygon mirror surface) of the optical deflector 15.

  Each light beam deflected by the optical deflector 15 is imaged by the scanning imaging lens 17 and collected as a light spot on the surface of the photosensitive drum 901 at a position spaced apart from each other in the sub-scanning direction. Lighted.

  The light deflector 15 is rotated at a constant speed by a polygon motor (not shown), and each light beam imaged in the vicinity of the deflecting reflection surface is deflected at a constant angular velocity along with the rotation. Each light spot on the body drum 901 moves at a constant speed in the main scanning direction. That is, two lines are simultaneously scanned on the photosensitive drum 901 in the main scanning direction.

  Further, a part of the light that passes through the scanning imaging lens 17 and goes outside the effective image area is received by the synchronization sensor 18 via the reflection mirror 19. The synchronous sensor 18 outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

  As shown in FIG. 10, the processing circuit includes a signal adjustment circuit 60, a modulation data generation circuit 30, a serial signal generation circuit 35, an image data generation circuit 40, a laser drive circuit 50, and the like.

  The signal adjustment circuit 60 amplifies, inverts, and binarizes the output signal of the synchronous sensor 18.

  The image data generation circuit 40 generates image data based on image information from the host device.

  The modulation data generation circuit 30 generates modulation data based on the signal from the signal adjustment circuit 60 and the image data from the image data generation circuit 40.

  The serial signal generation circuit 35 converts the modulation data from the modulation data generation circuit 30 into a serial signal.

  The laser drive circuit 50 generates drive signals for the single beam light sources LD1 and LD2 based on the serial signal from the serial signal generation circuit 35. Each drive signal generated here is output to the light source unit LU.

  Here, a method for manufacturing a grating having a sub-wavelength structure or a resonance structure (hereinafter also referred to as “fine structure grating”) will be described.

  The fine-structure grating has a period of about sub μm to several μm with respect to the wavelength region of visible light. There are not so many methods for manufacturing this fine-structured grating, and generally, a laser (interference) exposure method and an electron beam exposure method are widely used.

  In the laser interference exposure method, a laser beam having a wavelength in a blue to ultraviolet region is usually interfered and irradiated to a photosensitive polymer material (resist), and a microstructure lattice is produced using the interference pattern. In this case, a microstructure lattice is formed in the resist formed on the substrate. On the other hand, in the electron beam exposure method, a fine structure grating is produced by condensing an electron beam and scanning the resist. In this case as well, a fine lattice is formed in the resist applied on the substrate.

  In these methods, when a fine structure lattice is produced other than a resist (such as an optical element material such as quartz glass), reactive dry etching or lift-off is further performed based on the fine structure lattice formed in the resist. Must be used. The polarizing optical element 2 can be manufactured using the above general method.

  It is also possible to form a microstructure lattice directly on the optical element material instead of the resist. This method will be described with reference to FIGS.

  FIG. 11 shows an example using a photocuring method. The photo-curing method condenses laser light into a photo-curable material, cures the material in the vicinity of the condensing point by a multiphoton absorption process, and scans the laser light three-dimensionally to form a fine structure lattice. It is a method of producing. Laser light emitted from a laser device such as an Nd: YAG laser or a Ti: Sapphire laser is adjusted in waveform by a spatial filter after its light intensity is adjusted by a half-wave plate and a Glan-Thompson prism. Then, while changing the optical path by the galvanometer mirror, the light is condensed into the photocurable material on the substrate through the relay lens, the imaging lens, and the objective lens. Further, the condensing point can be moved in the direction perpendicular to the substrate by a piezo stage. Thus, it is possible to produce a three-dimensionally uneven microstructure by combining a galvanometer mirror and a piezo stage. At this time, the photocurable material includes a photocurable resin, a photocurable organic / inorganic hybrid material, and the like, and this photocurable material can function as an optical element as it is. Note that the processing apparatus shown in FIG. 11 is an example and is not limited to this.

  There is also a processing method using a laser ablation method. As the laser ablation method, a laser beam used for processing is made to interfere and an optical element material is directly processed by the interference pattern, or laser light is directly applied to an optical element material to be processed as shown in FIG. There is a method of selectively removing a part of the irradiation. Hereinafter, a description will be given with reference to FIG.

  A part of the laser light emitted from the laser device is transmitted through the photomask, and the laser light pattern is reduced and projected by the condenser lens through the mirror and irradiated onto the optical element material. The optical element material is installed on an XYZ stage and can be moved three-dimensionally. Of course, a galvanometer mirror or the like may be provided instead of the mirror, and the laser beam may be scanned. Further, a plurality of patterns (two types in FIG. 12) are prepared for the photomask, and can be selected according to the pattern to be processed, the optical element material to be processed, or the like. The movement of these XYZ stages and the selection of patterns are controlled by a PC (personal computer). Needless to say, the processing apparatus shown in FIG. 12 is an example.

  In any of the above processing methods, an ultrashort pulse laser having a laser beam pulse width of 10 picoseconds or less can be used. The use of an ultrashort pulse laser has advantages such as melting by heat propagation, reduction of damaged layer, and increase of multiphoton absorption cross section, and it has been used in recent years. In addition, since the multiphoton absorption cross-sectional area can be increased, the photocuring method can be more effectively processed with low energy.

  As is clear from the above description, in the optical scanning device 900 according to the present embodiment, a multi-beam light source unit is realized by the light source unit LU. The first light source is realized by the single beam light source LD1, the second light source is realized by the single beam light source LD2, the first optical system is realized by the lens 1, and the second optical system is realized by the lens 4. Thus, a deflection optical element is realized by the diffractive optical element 3, a polarization diffraction element is realized by the polarizing optical element 2, and a third optical system is realized by the λ / 2 plate 5.

  In the laser printer 100 according to the present embodiment, the charging device is constituted by the charging charger 902, the developing roller 903, the toner cartridge 904, and the transfer charger 911.

  As described above, according to the light source unit LU according to the present embodiment, the TM-polarized light beam emitted from the single beam light source LD1 is shaped by the lens 1 and then made TE-polarized by the λ / 2 plate 5. , Enters the polarizing optical element 2. On the other hand, the TM-polarized light beam emitted from the single beam light source LD 2 is deflected by the diffractive optical element 3, then shaped by the lens 4, and enters the polarizing optical element 2. The light beams incident on the polarization optical element 2 are emitted in the same direction. Therefore, the incident direction of each light beam incident on the polarizing optical element 2 can be arbitrarily set, and a plurality of light beams can be stably emitted without causing an increase in size and cost. .

  Further, according to the optical scanning device 900 according to the present embodiment, since the light source unit LU is used, as a result, a large number of lights are used on the surface to be scanned with high accuracy without causing an increase in size and cost. Can be scanned.

  Further, according to the laser printer 100 according to the present embodiment, since the optical scanning device 900 is provided, it is possible to form a high quality image at high speed without incurring an increase in size and cost. Become.

  In the above embodiment, as shown in FIG. 13 as an example, the single beam light source LD2 and the diffractive optical element 3 may be integrated. The semiconductor laser is usually packaged for the purpose of dust-proofing its light emitting part and sealed with a cover glass. Therefore, a function equivalent to that of the diffractive optical element 3 may be added to the cover glass. As a result, the number of parts can be reduced, and the space between the single beam light source LD2 and the lens 4 can be given a degree of freedom, and a merit in element layout can also be produced. In this case, as an example, the diffractive optical element 3 may be disposed obliquely as shown in FIG.

  In the above embodiment, the polarization state of the light beam is converted using the λ / 2 plate 5, but the present invention is not limited to this. In short, it is sufficient that the polarization direction of the light beam is changed by 90 °.

  In the above-described embodiment, the case where TM polarized light is emitted from each single beam light source is described. However, the present invention is not limited to this, and TE polarized light may be emitted from each single beam light source. However, in this case, instead of the polarizing optical element 2, when TM polarized light is incident, most of it is transmitted as 0th order light (0T), and when TE polarized light is incident, most of it is −1. A polarizing optical element that diffracts as the next light (-1T) is used.

  Moreover, in the said embodiment, as FIG. 15 shows as an example, you may radiate | emit TE polarized light from single beam light source LD1. As a result, the λ / 2 plate 5 becomes unnecessary.

  Moreover, although the case where the lens 1 was used as a 1st optical system was demonstrated in the said embodiment, it is not restricted to this, For example, a mirror may be used. Furthermore, the first optical system may be composed of a plurality of optical elements.

  Moreover, although the case where the lens 4 was used as a 2nd optical system was demonstrated in the said embodiment, it is not restricted to this, For example, a mirror may be used. Furthermore, the second optical system may be composed of a plurality of optical elements.

  Moreover, although the said light source unit LU demonstrated the case where the 1st light beam and the 2nd light beam were radiate | emitted in the substantially the same direction in the said embodiment, it is not limited to this, 1st light The beam and the second light beam may be emitted in different directions.

  In the above embodiment, the case where the image forming apparatus is the laser printer 100 has been described. However, the present invention is not limited to this. In short, an image forming apparatus provided with the optical scanning device 900 can form a high-quality image at high speed without causing an increase in size and cost.

  Further, even in an image forming apparatus that forms a color image, a high-quality image can be formed at high speed without causing an increase in size and cost by using an optical scanning device corresponding to the color image. It becomes possible.

  The image forming apparatus may be a tandem color machine that corresponds to a color image and includes a photosensitive drum for each piece of image information. FIG. 16 shows an optical scanning device in which two light source units LU are arranged facing the optical deflector 15. With this configuration, since two light beams are emitted from one light source unit LU, a total of four light beams are emitted toward the optical deflector 15, and each light beam is for each color of YMCK. The photosensitive drum provided can be scanned. In an actual image forming apparatus, a folding mirror is inserted between the scanning imaging lens 17 and the surface to be scanned, and each light beam is guided to the corresponding photosensitive drum. The figure is omitted.

  FIG. 17 shows an optical scanning device in which two light source units LU are arranged at an angle with respect to one reflecting surface of the optical deflector 15. In this case as well, a total of four light beams are emitted toward the optical deflector 15, and each light beam can scan on the photosensitive drum of the corresponding color.

  By using a laser array light source having two light emitting points in one package in place of each single beam light source, a total of eight light beams are emitted toward the optical deflector 15 and each color photoconductor. Two drums can be scanned. Further, by using a laser array light source having four light emitting points in one package, a total of 16 light beams are emitted toward the optical deflector 15 and can be scanned four by four on each color photosensitive drum. it can. As a result, a higher-speed image forming apparatus can be realized.

It is a figure for demonstrating schematic structure of the laser printer which concerns on one Embodiment of this invention. It is the schematic which shows the optical scanning device in FIG. It is a figure for demonstrating the light source unit in FIG. It is a figure for demonstrating the light radiate | emitted from each single beam light source in FIG. It is a figure for demonstrating the polarizing optical element in FIG. FIG. 6 is a diagram (part 1) for explaining the operation of the polarizing optical element of FIG. 5; FIG. 6 is a diagram (part 2) for explaining the operation of the polarizing optical element of FIG. 5; It is a figure for demonstrating the change of the diffraction angle in a diffractive optical element by a wavelength change. It is a figure for demonstrating the relationship between a polarizing optical element and a diffractive optical element. It is a figure for demonstrating a processing circuit. It is a figure for demonstrating the manufacturing method 1 of a polarizing optical element. It is a figure for demonstrating the manufacturing method 2 of a polarizing optical element. It is FIG. (1) for demonstrating integration of a single beam light source and a diffractive optical element. It is FIG. (2) for demonstrating integration of a single beam light source and a diffractive optical element. It is a figure for demonstrating the modification of the light source unit of FIG. It is a figure for demonstrating the optical scanning device (the 1) which can be used for a tandem color machine. It is a figure for demonstrating the optical scanning device (the 2) which can be used for a tandem color machine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens (1st optical system), 2 ... Polarization optical element (polarization diffraction element), 3 ... Diffraction optical element (deflection optical element), 4 ... Lens (2nd optical system), 5 ... (lambda) / 2 board (Third optical system), 100 ... laser printer (image forming apparatus), 900 ... optical scanning device, 901 ... photosensitive drum (scanning object), 902 ... charging charger (part of transfer device), 903 ... development Roller (part of transfer device), 904... Toner cartridge (part of transfer device), 909... Fixing roller (part of transfer device), 911... Transfer charger (part of transfer device), 913. (Transfer object), LD1... Single beam light source (first light source), LD2... Single beam light source (second light source), LU... Light source unit (multi-beam light source unit).

Claims (10)

A plurality of light sources including a first light source and a second light source that emit light beams having different polarization directions;
A first optical system for shaping a light beam emitted from the first light source;
A deflecting optical element for deflecting a light beam emitted from the second light source;
A second optical system for shaping the light beam deflected by the deflecting optical element;
A light beam that has passed through the first optical system and a light beam that has passed through the second optical system are incident, and at least part of the light beam that has passed through the first optical system and the second optical system a polarization diffraction element for emitting at least a portion of the through light beam in the same direction; equipped with,
The deflection optical element is a diffractive optical element;
A multi-beam light source unit in which the emission direction of at least a part of the light beam emitted from the polarization diffraction element via the second optical system does not depend on the wavelength of the light beam . A plurality of light sources including a first light source and a second light source that emit light beams having the same polarization direction;
A first optical system for shaping a light beam emitted from the first light source;
A deflecting optical element for deflecting a light beam emitted from the second light source;
A second optical system for shaping the light beam deflected by the deflecting optical element;
A light beam that has passed through the first optical system and a light beam that has passed through the second optical system are incident, and at least part of the light beam that has passed through the first optical system and the second optical system A polarization diffraction element that emits at least a part of the light beam through the same direction in the same direction;
Two light beams that are arranged on an optical path between the first light source and the polarization diffraction element or on an optical path between the second light source and the polarization diffraction element and are incident on the polarization diffraction element. as the polarization directions are different from each other, a third optical system for changing the polarization direction of the incident light and, with a
The deflection optical element is a diffractive optical element;
A multi-beam light source unit in which the emission direction of at least a part of the light beam emitted from the polarization diffraction element via the second optical system does not depend on the wavelength of the light beam . The relationship of m1 / Λ1 + m2 / Λ2 = 0 is satisfied using the diffraction order m1 in the polarization diffraction element, the grating period Λ1 of the diffraction grating, the diffraction order m2 in the deflection optical element, and the grating period Λ2 of the diffraction grating. The multi-beam light source unit according to claim 1 or 2. When the wavelength of the light beam from the second light source changes from λ to λ ″, the emission angle θ2 ″ of the light beam from the second light source in the deflection optical element and the light from the second light source The relationship of sinθ2 "-sinψ = (λ" -λ) (m1 / Λ1 + m2 / Λ2) is satisfied by using an incident angle ψ of the beam to the polarization diffraction element. Multi-beam light source unit. The multi-beam light source unit according to any one of claims 1 to 4, wherein the polarization diffraction element includes a diffraction grating that exhibits structural birefringence. The optical deflector及 beauty the polarization diffraction element is a multi-beam light source unit according to any one of claims 1 to 5 grating period of each grating is different from each other. The multi-beam light source unit according to any one of claims 1 to 6 , wherein the second light source and the deflecting optical element are integrated. In an optical scanning device that scans a surface to be scanned while deflecting a plurality of light beams including image information by a deflector,
Wherein the plurality of light beams, an optical scanning device which is a plurality of light beams emitted from the multi-beam light source unit according to any one of the at least one of claims 1 to 7. At least one scan object;
9. The optical scanning device according to claim 8 , wherein the optical scanning device scans a plurality of light beams with respect to the at least one scanning object;
An image forming apparatus comprising: a transfer device that transfers an image formed on the at least one scanning object to the transfer object. The image forming apparatus according to claim 9 , wherein the image information is color image information.

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