JP5086852B2 - Diffractive optical element and method - Google Patents

Description

  The present invention relates to a diffractive optical element having a fine step-like pattern on the surface, a processing accuracy evaluation method for the diffractive optical element, a processing method for a mold for forming a diffractive optical element, and the like.

  When the various lenses used in the optical scanning device are made of resin material, the resin lens is lightweight and can be formed at low cost, and it is easy to form special surface shapes typified by aspherical surfaces. By adopting a special surface for the manufactured lens, the optical characteristics can be improved and the number of lenses constituting the optical system can be reduced.

  On the other hand, as is well known, the resin lens changes its shape and refractive index with changes in the environment, especially temperature, so its optical characteristics, especially its power (condensing power), are designed. There is a problem that the “beam spot diameter”, which is the diameter of the light spot on the surface to be scanned, varies due to environmental fluctuations.

  Patent Document 1 discloses an optical scanning device (laser scanning device) that employs a diffractive surface having power and stabilizes optical properties in consideration of changes in optical properties associated with temperature changes and wavelength changes in a light source. Are known. In this patent document 1, it is implemented by an optical element in front of a polygon mirror of an optical scanning device for an optical printer or a digital copying machine, and has no power while the light source wavelength is maintained at the reference wavelength, and is caused by temperature disturbance. A coupling lens having a step-like concentric diffractive surface, which has power only when the wavelength is shifted, and a cylinder lens are applied.

  When manufacturing a resin-made diffractive lens, it is common to form a diffractive surface shape on a mold and transfer-mold the diffractive surface shape onto the lens surface by an injection molding method. Conventionally, cutting and dry etching have been performed to form a diffractive surface shape on a mold. For example, Patent Document 2 discloses an example in which a prism group element mold is manufactured by a cutting method.

In Patent Document 2, as shown in FIG. 13, a pattern P that looks linear when viewed from the direction of the optical axis L is formed, and the cross-sectional shape that includes the optical axis L and is cut by a plane perpendicular to the pattern P is formed on both sides. The diffractive optical element 1 having a high and low step shape at the center is targeted. The diffractive optical element 1 has a diffractive surface 1A on the top surface and a standing wall 1B on which both end portions of the diffractive surface 1A stand. In order to manufacture such a mold for transferring the diffractive optical element 1, as shown in FIG. 14, the sizes a and b of the bottom surface are the sizes a ′ and b ′ of the element surface of the diffractive optical element 1, respectively. A mold member 2 having the same dimensions as the above is prepared. Then, by setting the diamond cutting tool 3 at a position away from the mold member 2 and scanning the diamond cutting tool 3 along the tool path indicated by the arrow A, a stepped pattern P ′ is processed on the mold member 2. The
JP 2006-135069 A JP 2005-037623 A

  However, the cylinder lens used in the optical scanning device has an optical surface of about several millimeters, and the size of the element surface (particularly a ′) of the diffractive optical element 1 is the size of the bottom surface of the mold member 2 as in Patent Document 2. If the size is the same as that a, the diffractive optical element 1 becomes too small, the assemblability becomes very poor, and it is difficult to ensure the perpendicularity between the diffractive surface 1A and the standing wall 1B.

  Further, in the mold for molding the diffractive optical element 1 (that is, the processed mold member 2), the diffractive surface molding portion of the mold once used for molding (the diffractive surface 1A of the diffractive optical element 1 is molded). For example, when reworking to correct the part), the setting takes a lot of time and a lot of loss has occurred.

  An object of the present invention is to provide a diffractive optical element that is highly accurate and excellent in assemblability, as well as a method for evaluating the processing accuracy of the diffractive optical element, and to process a mold for forming a diffractive optical element without taking time It is in providing the processing method which can be performed.

  In order to solve the above-described problems, in the present invention, in the diffractive optical element molding die, the depth of both ends of the diffractive surface molded part is determined when the diffractive surface molded part for molding the diffractive surface of the diffractive optical element is processed. Provide an approach part (inclined surface molding part) that gradually becomes deeper. Accordingly, the dimension of the mold member (mold) that forms the optical surface (diffractive surface) of the diffractive optical element can be freely set independently of the optical surface dimension. For example, by enlarging the mold member, parallel adjustment when assembling the mold becomes easy, but the processing machine can be easily and accurately attached when reworking the optical surface, and the outer peripheral height of the diffraction surface is easy. Can be used for lens thickness management. As a result, a highly accurate diffractive optical element can be manufactured with high efficiency. In addition, in a diffractive optical element, not only a sloped surface for approach, but also observation of a corner where three planes (a diffractive surface, an inclined surface, and a step surface that is a standing surface of the diffractive surface or the inclined surface) intersect. Thus, an element shape that can be used as a simple checker for transferability evaluation and can be used for quality control during mass production is realized.

  That is, according to the first aspect of the present invention, a pattern that looks linear when viewed from the optical axis direction is formed, and the cross-sectional shape that is cut by a plane that includes the optical axis and is perpendicular to the pattern is high at both sides and at the center. A diffractive optical element that is low or has a step shape that is low on both sides and high in the center, and when each region sandwiched between the patterns is a linear ring zone, each linear ring zone has a chevron shape. A band-like diffractive surface is formed on the upper surface, and band-shaped inclined surfaces are formed on both ends of the diffractive surface.

  According to a second aspect of the present invention, in the first aspect, an angle formed by the diffractive surface and the inclined surface is constant for each of the linear ring zones.

  According to a third aspect of the present invention, in the first or second aspect, the lens surface opposite to the lens surface on which the pattern is formed is provided with a cylinder surface having a cylinder central axis parallel to the pattern, and The both end portions of the cylinder surface are formed in a curved shape.

  According to a fourth aspect of the present invention, there is provided a light source, a coupling lens for coupling a light beam from the light source, a cylinder lens for making the light beam from the coupling lens parallel to the main scanning direction, and the cylinder lens. An optical deflector that deflects the light beam in the main scanning direction and a scanning lens that condenses the light beam deflected by the optical deflector. Alternatively, the diffractive optical element described in 3 is mounted.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus for forming an image by performing an electrophotographic process, wherein the optical scanning device according to the fourth aspect is mounted as means for performing an exposure process of the electrophotographic process. It is characterized by being.

In the invention of claim 6, when evaluating the processing accuracy of the diffractive optical element of claim 1, 2, or 3, a ridge formed by the diffractive surface and the inclined surface, the diffractive surface and the diffractive surface Observe the ridge line formed by the step surface that is a standing wall, the ridge line formed by the inclined surface and the step surface that is the standing wall, and the intersection of the three ridge lines, and the thickness of each ridge line and the The transfer level of the pattern is determined from the size of the intersection.

  The invention according to claim 7 is the case where the diffractive optical element according to claim 1 is manufactured by injection molding, and a single crystal diamond having a non-rotating linear ridge line when the injection molding die is processed. When the angle formed between the diffractive surface forming part for forming the diffractive surface and the inclined surface forming part for forming the inclined surface is set to θ using a cutting tool, θ ≦ 45 degrees is set. It is characterized by processing.

  The invention according to claim 8 is the case where the diffractive optical element according to claim 1 is manufactured by injection molding, and a single crystal diamond tool having a straight ridge line is rotated when the injection molding die is processed. On the surface of each molding part, using a fly-cut-shaped tool, and a diffractive surface molding part for molding the diffractive surface and an inclined surface molding part for molding the inclined surface. It is characterized by performing a cutting operation.

  According to the first aspect of the present invention, the dimension of the mold member forming the optical surface (diffraction surface) can be freely set independently of the optical surface dimension. For example, by enlarging the mold member, parallel adjustment at the time of mold assembly is facilitated. In addition, the processing machine can be easily and accurately attached when re-machining the optical surface, and in addition, the outer peripheral height of the diffractive surface can be easily measured, which can be utilized for lens thickness management. As a result, it is possible to manufacture a diffractive optical element with high accuracy and excellent assemblability. Furthermore, by making both end portions of the diffractive surface into inclined surfaces, the resin flow becomes smooth when the diffractive optical element is molded with resin.

  According to the second aspect of the present invention, by making the angle formed by the diffractive surface and the inclined surface constant, resin flow, transfer, and shrinkage without habit can be realized, and a highly accurate and highly stable diffractive optical element molding process Can be earned.

  According to the invention of claim 3, by making both ends of the cylinder surface into a curved surface shape, the resin flow becomes smooth when the diffractive optical element is molded with resin.

  According to the fourth aspect of the present invention, an optical scanning device that is resistant to temperature disturbance and has stable optical characteristics even when a resin-made scanning lens is used by adopting a diffractive surface having power in consideration of wavelength change in the light source. Can be obtained.

  According to the invention of claim 5, it is possible to realize an image forming apparatus that is resistant to temperature disturbance and has stable optical characteristics.

  According to the sixth aspect of the present invention, it can be used as a simple checker for transferability evaluation by observing a corner portion where three planes intersect, instead of simply using an inclined surface for approach, and can be used as an AFM (Atomic force Microscope). ) And so on, quality control during mass production can be carried out with high efficiency and at low cost.

  According to the seventh aspect of the present invention, it is possible to surely avoid tool interference by setting a value from the production limit of the diamond tool.

  According to the invention of claim 8, by using the fly cut tool, θ (angle formed by the diffractive surface forming portion and the inclined surface forming portion) can be set as a free tool path without worrying about tool interference. . In addition, since the cutting resistance can be remarkably reduced as compared with a non-rotating tool, it can be applied to a low-rigidity member such as a resin as an element processing rather than a workpiece or mold processing in which the cutting resistance is a problem.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 show a diffractive optical element according to the present invention. FIG. 1 is an external perspective view, and FIG. 2 (a) is a top view. FIGS. 2B and 2C are enlarged views of a portion B in FIG.

  As shown in FIG. 1 and FIG. 2A, the diffractive optical element 10 according to the present invention has a pattern P that looks linear when viewed from the direction of the optical axis L, and is a plane that includes the optical axis L and is perpendicular to the pattern P. The cross-sectional shape cut by S forms a staircase shape that is high at both sides and low at the center.

  And when each area | region pinched | interposed by the pattern P is made into the linear ring zone parts 11-19, each linear ring zone parts 11-19 comprise the mountain shape, and are formed on the base board 20. As shown in FIG. The straight ring zone part 11 and the straight ring zone part 19 have the same width (length along the plane S: the same applies hereinafter), and the straight ring zone part 12, the straight ring zone part 18, the straight ring zone part 13 and the like. The straight ring zone part 17, the straight ring zone part 14 and the straight ring zone part 16 have the same width. The width of the straight ring zone 15 is the widest, and the straight ring zone 14 and the straight ring zone 16, the straight ring zone 13 and the straight ring zone 17, the straight ring zone 12 and the straight ring zone 18 in the following order. It becomes narrow, and the linear ring zone part 11 and the linear ring zone part 19 are the narrowest.

  On the other hand, the height of the linear zone part 11 and the linear zone part 19 is highest, and hereinafter, the linear zone part 12 and the linear zone part 18, the linear zone part 13 and the linear zone part 17, and the linear zone part. 14 and the linear zone part 16 become lower in order, and the linear zone part 15 is the lowest. The linear ring zones 11 to 19 are integrally formed.

  The straight annular zone 11 is formed with a belt-like diffractive surface 11A on its upper surface, and strip-like inclined surfaces 11B and 11C are formed at both ends of the diffractive surface 11A. The straight annular zone 12 has a belt-like diffraction surface on its upper surface. The surface 12A is formed with band-shaped inclined surfaces 12B and 12C at both ends of the diffractive surface 12A. Further, the linear ring zone portion 13 is formed with a band-like diffractive surface 13A on the upper surface thereof, and band-like inclined surfaces 13B and 13C are formed at both ends of the diffraction surface 13A, respectively. The diffraction surface 14A is formed with band-shaped inclined surfaces 14B and 14C at both ends of the diffraction surface 14A. Further, the linear ring zone portion 15 is formed with a band-like diffractive surface 15A on its upper surface and band-like inclined surfaces 15B and 15C on both ends of the diffractive surface 15A.

  Further, the linear ring zone part 16 is formed with a band-like diffractive surface 16A on the upper surface thereof, and band-like inclined surfaces 16B and 16C are formed at both ends of the diffraction surface 16A, respectively. The diffraction surface 17A is formed with band-shaped inclined surfaces 17B and 17C at both ends of the diffraction surface 17A. Further, the linear ring zone portion 18 is formed with a band-like diffractive surface 18A on the upper surface thereof, and band-like inclined surfaces 18B and 18C are formed at both ends of the diffraction surface 18A, respectively. The diffraction surface 19A is formed with band-shaped inclined surfaces 19B and 19C at both ends of the diffraction surface 19A.

  About each linear ring zone part 11-19, the angle which a diffraction surface and an inclined surface comprise is constant. That is, the angle formed between the diffractive surface 11A and the inclined surface 11B and the angle formed between the diffractive surface 11A and the inclined surface 11C with respect to the straight annular zone 11, and the angle between the diffractive surface 12A and the inclined surface 12B with respect to the linear annular zone 12 are formed. The angle formed between the diffractive surface 12A and the inclined surface 12C, the angle formed between the diffractive surface 13A and the inclined surface 13B and the angle formed between the diffractive surface 13A and the inclined surface 13C with respect to the linear annular zone 13, and the linear annular zone 14 The angle formed by the diffraction surface 14A and the inclined surface 14B and the angle formed by the diffraction surface 14A and the inclined surface 14C are constant. In addition, the angle formed by the diffractive surface 15A and the inclined surface 15B and the angle formed by the diffractive surface 15A and the inclined surface 15C with respect to the straight annular zone 15 are the same as the predetermined angle.

  Furthermore, the angle formed by the diffractive surface 16A and the inclined surface 16B with respect to the linear ring zone portion 16 and the angle formed between the diffractive surface 16A and the inclined surface 16C, and the angle formed between the diffractive surface 17A and the inclined surface 17B with respect to the linear ring zone portion 17 are formed. The angle formed by the diffraction surface 17A and the inclined surface 17C, the angle formed by the diffraction surface 18A and the inclined surface 18B, and the angle formed by the diffraction surface 18A and the inclined surface 18C, and the linear ring portion 19 The angle formed by the diffractive surface 19A and the inclined surface 19B and the angle formed by the diffractive surface 19A and the inclined surface 19C are the same as the predetermined angle.

  Moreover, about the linear ring zone parts 11-19, the length of the longitudinal direction of a diffraction surface is the same. That is, the lengths of the diffractive surfaces 11A, 12A, 13A, 14A, 15A, 16A, 17A, 18A and 19A in the longitudinal direction are the same.

  And the height of the linear ring zones 11 and 19 is the highest, and the linear ring zones 12 and 18, the linear ring zones 13 and 17, the linear ring zones 14 and 16, and the linear ring zone 15 become lower in this order. Therefore, the inclined surfaces 11B and 19B are arranged so as to protrude on the outermost side (left side in FIG. 2) on the base 20, and hereinafter, the protruding amounts of the inclined surfaces 12B and 18B, the inclined surfaces 13B and 17B, and the inclined surfaces 14B and 16B in this order. And the protruding amount of the inclined surface 15B is the smallest. Similarly, the inclined surfaces 11C and 19C are arranged so as to protrude on the outermost side (right side in FIG. 2) on the base 20, and hereinafter, the protruding amounts of the inclined surfaces 12C and 18C, the inclined surfaces 13C and 17C, and the inclined surfaces 14C and 16C in this order. And the protruding amount of the inclined surface 15C is the smallest.

  In the diffractive optical element 10 having the above configuration, the optical functions are provided by the diffractive surfaces 11A to 19A, and the incident light beam passes through the regions of the diffractive surfaces 11A to 19A. When emphasizing transferability, the flow direction of the resin is often parallel to the diffraction pattern. In such a case, as described above, the angle formed by the diffraction surfaces 11A to 19A and the inclined surfaces 11B to 19B, In addition, it is more advantageous to ensure transferability and uniform shrinkage when the angle formed by the diffraction surfaces 11A to 19A and the inclined surfaces 11C to 19C is constant.

  2 (b) and 2 (c) show a ridge line 21 formed by the diffractive surface 13A and the inclined surface 13C, a ridge line 22 formed by the diffractive surface 13A and a stepped surface (not shown) which is a standing wall thereof, This is an enlarged view of a ridge line 23 formed by an inclined surface 13C and a step surface (not shown) which is a standing wall, and an intersection 24 of the three ridge lines 21, 22, and 23. Thus, the corner portion where the three surfaces intersect is a portion that is difficult to be completely filled with the resin, and is a portion that is sensitive to poor filling. When this corner is observed with an optical microscope, when the filling is complete, a clean cross line is confirmed as shown in FIG. 2 (b), the transfer is good, but the filling is insufficient. In this case, as shown in FIG. 2C, an unfilled area is confirmed at the intersection 24, and good transfer cannot be obtained.

  Therefore, by setting the threshold values of the thickness of the ridge lines 21, 22, 23 and the size of the intersection 24, it is possible to easily monitor the molding state during mass production. Conventionally, transfer defects such as corner sagging have been inspected with an AFM (Atomic Force Microscope) or the like and required a very long time, which is not practical.

  FIG. 3 is an external perspective view of a mold 25 for forming the linear ring zones 11 to 19 (that is, the diffraction surfaces 11A to 19A and the inclined surfaces 11B to 19B and 11C to 19C). The mold 25 is formed with a concave portion 26 having a shape obtained by inverting the diffractive surfaces 11A to 19A and the inclined surfaces 11B to 19B and 11C to 19C. The base material of the mold 25 is martensitic stainless steel, and the molding surface is subjected to 150 μm-thick electroless Ni plating.

  In the portion for forming the linear annular zone portion 15, the depth of engraving of the diffractive surface 15A 'is 70 μm in total. The size of the diffractive surface 15A 'is 3 mm in the short side direction and 6 mm in the long side direction, and ends of inclined surfaces 15B' and 15C 'are formed at both ends thereof. Here, since the angle θ between the diffractive surface 15A ′ and the inclined surfaces 15B ′ and 15C ′ is set to 20 °, the engraving depth is 70 μm × tan 20 ° = 26 μm, and the end portions of the inclined surfaces 15B ′ and 15C ′. Is the length of the longest one, and does not unnecessarily increase the size of the molded product.

  FIG. 4 illustrates a method of processing the mold when a non-rotating tool is used. FIG. 5 is a schematic view of FIG. 4 viewed from the side.

  The single crystal diamond cutting tool 27 is positioned above the mold member 25 ′, and the mold member 25 ′ is cut obliquely at a predetermined angle. As shown by arrows C and D, the oblique tool path is a tool path for processing the end portion of the inclined surface, and the approach and retract of the tool are performed. An arrow E is a tool path for diffractive surface machining.

Here, the important point is to pay attention to the angle θ formed by the diffractive surface and the inclined surface. When the angle formed by the front relief surface 27a of the diamond tool 27 and the diffraction surface is φ,
θ <φ
If the relationship is not set, the front dented surface 27a and the end of the inclined surface interfere with each other at the time of the tool approach, and the cutting surface may become a peeling surface as well as cause damage to the tool. At present, the manufacturing limit of the single crystal bit is 30 ° in the front clearance angle, and the working posture is around −15 ° as the negative squeeze angle state. When these are combined, the combined limit is 45 °, and θ is 45 It is desirable to make it below °.

  According to this embodiment, the dimension of the mold member that forms the diffractive surface can be freely set independently of the optical surface dimension. For example, by making the mold member larger, parallel adjustment at the time of assembling the mold is possible. Becomes easy. In addition, the processing machine can be easily and accurately attached when re-machining the optical surface, and in addition, the outer peripheral height of the diffractive surface can be easily measured, which can be utilized for lens thickness management. As a result, it is possible to manufacture a diffractive optical element with high accuracy and excellent assemblability. Furthermore, by making both end portions of the diffractive surface into inclined surfaces, the resin flow becomes smooth when the diffractive optical element is molded with resin.

  6 and 7 show a state in which the diffractive optical element is turned over, FIG. 6 is a perspective view of the appearance thereof, and FIG. 7 is a side view of FIG.

  6 and 7 show an example in which the end slope is formed by a rotating tool. The lens surface opposite to the lens surface on which the pattern P (see FIG. 1) is formed is provided with a cylinder surface 28 having a cylinder central axis parallel to the pattern P, and curved surfaces at both ends of the cylinder surface 28. 28A and 28B are formed. Since the cylinder surface 28 is processed by R-cut fly cutting, the curved portions 28A and 28B are curved like a toric surface.

  In this example, both ends (both ends of the diffraction surface) of the linear annular zone 29 are not inclined surfaces but arcuate surfaces (cylinder surfaces) 29A and 29B.

  In the above embodiment, the diffractive optical element 10 has a stepped shape in which the cross-sectional shape on the plane S (see FIG. 1) is high at both sides and low at the center, but is not limited thereto. The cross-sectional shape on the plane S may be a stepped shape that is low on both sides and high on the center.

  FIG. 8 illustrates a method of processing a mold member with a rotary tool. As in the case of FIG. 4 and FIG. 5, the tool path is composed of those in the directions of arrows C and D for forming the inclined surface and those in the direction of arrow E for forming the diffractive surface. The difference from the non-rotating tool is that the interference of the front flank is determined by the turning radius of the rotating tool 30 and does not depend on the tool path. Therefore, θ as a tool path can be 90 °. However, since the rotation radius at the tip of the rotary tool 30 is at least about 3 mm, the end of the inclined surface becomes longer than the non-rotary tool. In the case of a rotating tool, it is necessary to take into consideration that θ as a tool path and θ as a machining surface do not match.

  FIG. 9 shows another embodiment of the diffractive optical element. In FIG. 9, the angle between the diffractive surfaces 11a to 19a and the inclined surfaces 11b to 19b and 11c to 19c is not constant, and the end portions of the inclined surfaces 11b to 19b and 11c to 19c are made uniform. There is. Other configurations are the same as those in FIGS. 1 and 2.

  If comprised in this way, it can utilize when the longitudinal dimension of an element has severe restrictions.

  In the case of FIG. 9 as well, the diffractive optical element 10 has a stepped shape in which the cross-sectional shape on the plane S (see FIG. 1) is high on both sides and low on the center, but is not limited thereto. The cross-sectional shape on the plane S may be a stepped shape that is low on both sides and high on the center.

FIG. 10 is a cross-sectional view schematically showing a mold 31 for molding a diffractive optical element by injection molding. The mold 31 includes a fixed mold 32 and a movable mold 33, and a space (cavity) for molding a diffractive optical element having a predetermined shape by coupling both the molds 32 and 33 together. ) 34 is formed. The movable mold 33 is provided with a resin injection port 35 for injecting a resin material into the space 34. The molding process of the diffractive optical element using this mold 31 is as follows.
(1) The molds 32 and 33 are heated to a molding temperature of about 130 to 140 degrees.
(2) The molten resin material is injected into the space 34 from the resin injection port 35 at a high pressure of 30 to 100 MPa.
(3) Cool the whole.
(4) When the temperature is lowered to an appropriate temperature, the fixed mold 32 and the movable mold 33 are separated.
(5) In the mold open state, the diffractive optical element is stuck to the movable mold 33.
(6) The diffractive optical element, which is a molded product made of resin, is pulled out in the direction of the optical axis (left side in the figure), and is pushed out by an ejector pin not shown.

  FIG. 11A is a configuration diagram of the first optical system mounted on the optical scanning device 40 shown in FIG. 12 and positioned in front of the polygon mirror 41 on the optical path. In FIG. 12, the configuration of the scanning lens 42 behind the polygon mirror 41 is the second optical system.

  As shown in FIG. 11A, the first optical system has a function of projecting divergent light from a semiconductor laser (LD) 43, which is a light source, onto the polygon mirror 41 as gentle convergent light. Laser light 44, which is diverging light from the LD 43, enters the diffraction surface 45 </ b> A of the coupling lens 45. As shown in FIG. 11B, the coupling lens 45 has a diffractive surface 45A having a concentric pattern.

  The exit surface 45B of the coupling lens 45 is a coaxial aspheric surface, and the laser light 44 passes through the aperture 46 and is formed into a desired beam shape, and then enters the cylinder surface 47A of the cylinder lens 47. Thereafter, the laser beam 44 is emitted from the emission surface 47B of the cylinder lens 47 as a gentle convergent light. As shown in FIG. 11C, the cylinder lens 47 has a diffractive surface 47B having a linear pattern. The cylinder lens 47 shown here is equivalent to the diffractive optical element 1 shown in FIG.

  The optical scanning device 40 can be applied to an image forming apparatus such as a printer.

1 is an external perspective view of a diffractive optical element according to the present invention. (A) is a top view of the diffractive optical element according to the present invention, and (b) and (c) are enlarged views of part B of (a). It is an external appearance perspective view of the metal mold | die for shape | molding the linear ring zone part of a diffractive optical element. It is a figure explaining the method of processing the metal mold | die shown in FIG. 3 using a non-rotating tool. FIG. 5 shows a method of machining a mold using a non-rotating tool, and is a view of FIG. 4 viewed from the side. It is an external appearance perspective view of a diffractive optical element when turned over. FIG. 7 is a side view of FIG. 6. It is a figure explaining the method of processing a mold member with a rotary tool. It is a top view of the diffractive optical element by another Example. It is a schematic diagram of the metal mold | die structure for shape | molding a cylinder lens. (A) is a block diagram of the 1st optical system located in front of the polygon mirror of an optical scanning device, (b) is a figure which shows the diffraction surface of the coupling lens arrange | positioned in a 1st optical system, (c) is 1st. It is a figure which shows the diffraction surface of the cylinder lens arrange | positioned at an optical system. It is a figure which shows the structure of an optical scanning device. It is an external appearance perspective view of the cylinder lens by a prior art. It is a figure explaining the method to process the metal mold | die for shape | molding the cylinder lens of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diffractive optical element 11-19 Linear ring part 11A-19A Diffraction surface 11B-19B, 11C-19C Inclined surface 21,22,23 Ridge line 24 Intersection 25 Mold 25 'type | mold member 27 Single crystal diamond bit 28 Cylinder surface 28A, 28B Curved portion 30 Rotating tool 40 Optical scanning device P Linear pattern

Claims (8)

A staircase pattern is formed that looks straight when viewed from the optical axis direction, and the cross-sectional shape cut by a plane that includes the optical axis and is perpendicular to the pattern is high at both sides and low at the center or low at both sides and high at the center A diffractive optical element having a shape,
When each region sandwiched between the patterns is a linear ring zone, each linear ring zone has a mountain shape, a band-like diffractive surface on the upper surface, and band-shaped inclined surfaces on both ends of the diffractive surface, respectively. A diffractive optical element formed.   2. The diffractive optical element according to claim 1, wherein an angle formed by the diffractive surface and the inclined surface is constant for each of the linear ring zones.   The lens surface opposite to the lens surface on which the pattern is formed is provided with a cylinder surface having a cylinder central axis parallel to the pattern, and both end portions of the cylinder surface are formed in a curved shape. The diffractive optical element according to claim 1 or 2. A light source, a coupling lens for coupling a light beam from the light source, a cylinder lens for making the light beam from the coupling lens parallel to the main scanning direction, and deflecting the light beam from the cylinder lens in the main scanning direction An optical scanning device comprising an optical deflector and a scanning lens for condensing a light beam deflected by the optical deflector,
An optical scanning device, wherein the diffractive optical element according to claim 1, 2 or 3 is mounted as the cylinder lens. An image forming apparatus that forms an image by performing an electrophotographic process,
An image forming apparatus comprising the optical scanning device according to claim 4 as means for performing an exposure process of an electrophotographic process. In evaluating the processing accuracy of the diffractive optical element according to claim 1, 2, or 3,
A ridge line formed by the diffractive surface and the inclined surface, a ridge line formed by the diffractive surface and a step surface that is a standing wall thereof, a ridge line formed by the inclined surface and a step surface that is a standing wall thereof, And a method for evaluating the processing accuracy of the diffractive optical element, wherein the intersection of the three ridge lines is observed, and the transfer level of the pattern is determined from the thickness of each ridge line and the size of the intersection.   When the diffractive optical element according to claim 1 is manufactured by injection molding, a single crystal diamond tool having a non-rotating linear ridge line is used when processing a mold for injection molding, and the diffraction surface Forming is performed by setting θ ≦ 45 degrees, where θ is an angle formed by a diffractive surface molding portion for forming the inclined surface and an inclined surface molding portion for forming the inclined surface. Mold processing method.   When the diffractive optical element according to claim 1 is manufactured by injection molding, when processing a mold for injection molding, a fly-cut tool in which a single crystal diamond tool having a straight ridge line is rotated is used. In addition, a cutting operation is performed on the surface of each molding part with respect to the diffraction surface molding part for molding the diffraction surface and the inclined surface molding part for molding the inclined surface. Processing method of mold for molding.

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