JP2005225089A - Method for producing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a manufacturing period and the date of delivery of an optical element to be short and early. <P>SOLUTION: The simulation of a releasing amount in addition to a design value is performed during the manufacture of a specular piece, shape data practically manufactured based on reference data on an analogous optical element are carried out, and processing is done based on this value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a manufacturing method for molding an optical element with an optical resin, and is effective mainly for an optical element of a scanning optical system employed in an optical scanning device mounted on a copying machine or a printer. It is.

  In recent years, an optical resin has been frequently used instead of a glass material that has been employed in laser scanning systems such as copying machines and printers.

  An optical element made of optical resin is manufactured by injection molding using a mold, but has a high degree of freedom in setting the surface shape, which is an advantage of the optical resin, but has a problem that manufacturing errors are likely to occur. Until now, various methods have been proposed for this problem.

  For example, in Patent Document 1, it is effective for resin shrinkage that occurs during molding. First, the amount of resin shrinkage is determined in the first molding, the correction amount is calculated for the result, and the final gold The mold shape is determined.

  Further, in the confirmation of the optical performance obtained by molding, as described in Patent Document 2, the condensing positions of the light beams in the main scanning and the sub scanning are obtained, and at that time, the deviation in the sub scanning direction of the light beams is further determined. There has been proposed a method of manufacturing a higher-performance optical element by performing a measurement taking into consideration the light collection position in the optical axis direction and the curvature of the scanning line, such as obtaining the distribution.

  FIG. 5 is a flowchart of a conventional method for manufacturing an optical element.

  First, optical design (a) of the optical element to be manufactured is performed.

  Based on this design value, a mirror face piece is created (b), and initial molding (c) of the first optical element is performed.

  An optical scanning device having the same conditions as the actual use of the optical element obtained by the initial molding is prepared, and the optical characteristics are measured using the optical scanning device (d).

  If the obtained measurement value is within the allowable range compared with the design value, the process is completed (h). However, if it is determined that the measurement value exceeds the allowable range, the optical design is redesigned (e). Do.

  The redesign is performed by calculating a correction amount for the mirror surface piece, and the mirror surface piece is corrected (f) by this correction amount and the main forming (g) is performed.

  Then, measurement (d) of the optical characteristic is performed again to determine whether correction is performed again.

In this way, when the finally satisfying performance is obtained, the process is completed. However, in many cases, the performance is not satisfied once, and the process is usually repeated several times.
JP-A-5-96572 JP 2003-94441 A

  As described above, although the above proposals are also effective methods, they are premised on repeated corrections.

  Although it is difficult to always make this repetition zero, if the number of corrections increases, the production schedule naturally increases, which affects the development and production of devices that use the optical element, and the cost of that amount. Therefore, it has been desired that the user should do as few times as possible.

  In this proposal, in order to increase the accuracy of the finish at the time of molding and reduce the number of corrections of the mold as much as possible, the manufacturing method is further devised, cost reduction by reducing the number of corrections of the mold, In addition, it is possible to shorten the manufacturing schedule, and to take into account factors such as scanning line curvature of the scanning optical system and other factors that depend on the shape error and refractive index distribution that cause curvature of field, etc. The object is to provide a method for manufacturing an optical element that can be manufactured.

The method for manufacturing an optical element according to claim 1, with respect to the problem,
This is a method for manufacturing an optical element from an optical resin, a molding condition determining step for setting conditions under which stable molding can be performed from a shape based on optical design values, and a mold release amount calculated and predicted based on the shape and molding conditions of the optical element. It is characterized by comprising a mold quantity simulation step, a specular piece production step for producing a specular piece based on the simulation result, and a forming step for forming using the specular piece.

The method for producing an optical element according to claim 2 comprises:
An initial molding step for molding an optical element by the method according to claim 1, an optical performance measuring step for measuring optical characteristics of the optical element, and obtaining a target optical performance from the optical performance measured in the optical characteristic measuring step. For this purpose, a redesign step for correcting the surface shape, a specular piece correction step for correcting and correcting the specular piece based on the correction value obtained in the redesign step, and re-molding with the corrected specular piece It is characterized by comprising the main forming step.

The method for producing an optical element according to claim 3 comprises:
It is a manufacturing method of the optical element according to claim 1.
The mold release amount simulation step is characterized by calculating a mold release prediction amount obtained by simulation calculation including at least one of parameters of a resin temperature during molding, an injection pressure, and a temperature distribution of the mold.

The method for producing an optical element according to claim 4 comprises:
It is a manufacturing method of the optical element according to claim 1.
The mold release amount simulation step is characterized in that a mold release prediction amount is calculated by performing a simulation calculation based on molding conditions of an optical element having a similar shape.

The method for producing an optical element according to claim 5,
It is a manufacturing method of the optical element according to claim 2.
The specular frame correction step is repeatedly performed from the optical property measurement step so that the measurement value obtained by the optical performance measurement step or the optical performance obtained by optical simulation based on the measurement value becomes a desired value. .

The method for producing an optical element according to claim 6 comprises:
It is a manufacturing method of the optical element according to claim 2.
The optical performance measuring step is characterized in that it includes shape measurement including a mirror surface shape of the molded optical element and measurement of an image formation state of a light beam by the optical element.

The method for producing an optical element according to claim 7 comprises:
It is a manufacturing method of the optical element according to claim 2.
The optical characteristic measurement step obtains a focus position in a main scanning direction of a light beam at a plurality of main scanning image heights by the optical element with respect to a specified image plane in the measurement, and a deviation amount in the optical axis direction with respect to the specified image plane. It is characterized by seeking.

The method for producing an optical element according to claim 8 comprises:
It is a manufacturing method of the optical element according to claim 2.
The optical characteristic measuring step obtains a focus position in a sub-scanning direction of a light beam at a plurality of main scanning image heights by the optical element with respect to a prescribed image plane in the measurement, and in the optical axis direction with respect to the prescribed image plane. It is characterized by obtaining a deviation amount.

The method for producing an optical element according to claim 9 comprises:
It is a manufacturing method of the optical element according to claim 7 and 8,
The focus position is measured at a plurality of light beam diameters in the vicinity of the prescribed image plane in the optical axis direction, and two positions where the light beam diameter distribution is equal to or smaller than a predetermined light beam diameter in the main scanning and sub-scanning are obtained. It is characterized in that the two intermediate points are obtained as the focus positions of the main scanning and the sub scanning.

The method for producing an optical element according to claim 10 comprises:
It is a manufacturing method of the optical element according to claim 2.
In the redesign step, the mirror surface shape error obtained in the optical performance measurement step and the optical performance obtained from the measurement result of the imaging state of the light beam by the optical element are combined, and the optical performance is a desired performance. It is characterized in that a shape correction value for the shape error is calculated.

The method for producing an optical element according to claim 11 is:
It is a manufacturing method of the optical element according to claim 2.
In the redesign process, correction is performed on any one or more of field curvature, scanning line curvature, magnification error, fθ characteristic, and beam diameter as optical performance.

An optical element for an optical scanning device of an optical element according to claim 12,
It is manufactured using the manufacturing method according to any one of claims 1 to 11.

  As described above, when creating a mirror face piece, in addition to the design value, the mold release amount simulation and the shape data actually produced based on the reference data of similar optical elements are created and processed based on this value. Since the provisional manufacturing process is omitted, the manufacturing period and delivery time can be set short, and more rapid development and manufacturing are possible.

  In addition, since the number of repetitions of correction is reduced, the cost can be reduced, and unstable elements can be reduced in manufacturing accuracy, so that a more accurate optical element can be provided.

(Embodiment 1)
Hereinafter, the first embodiment of the present proposal will be described in detail.

  FIG. 1 shows a flow of a method of manufacturing an optical element using an optical resin according to the present invention. First, the overall flow will be described with reference to this drawing.

  First, the optical design (a) of the optical element to be manufactured is performed, and the data for the mirror surface piece is created by adding a simulation result for correcting the release amount described later to the optical surface shape based on the design value. (B).

Then, a mirror piece based on this data is created (c) and initial molding (d) is performed. (End of initial molding process)
Next, the shape and optical characteristics of the molded optical element are measured and compared with the design values (e). If the shape and optical characteristics are within the specified tolerances, the process is completed (q: END). If there is an error, further correction is performed. (End of optical property measurement process)
Hereinafter, the procedure for correcting the main scanning will be described.

  First, a difference from the design value at each position along the main scanning direction of the optical element is calculated from the obtained surface shape data.

  Divide the main scanning direction into an appropriate range (several mm), create an approximate polynomial in each divided range from the data, calculate the partial curvature of each polynomial by its second derivative (f), connect it to graph To do.

  A polynomial representing the curve of this graph is calculated and modeled (g).

  In this way, when the difference from the design value is obtained, the model formula is not modeled, but it is possible to capture a minute change by using the partial curvature notation by the second derivative, and more accurate correction is possible. Because.

  Then, by performing quadratic integration of the polynomial again, a polynomial that expresses the difference in surface shape in detail can be obtained.

  If the parameters of the polynomial are set so that there is no difference from the design value, a polynomial representing the corrected shape can be obtained, and the temporarily corrected shape can be calculated (h).

  The image plane simulated by the obtained polynomial is compared with the image plane based on the original design value, and, for example, the curvature of the image plane or the curvature of the scanning line is calculated to evaluate whether a desired optical characteristic can be obtained. (I).

  If it is determined that the desired optical performance can be obtained from this result, the mirror piece is corrected based on the result (o) and the main molding (p) is performed. However, in some cases, the desired performance is almost obtained. However, it may be judged that there is still room for correction for a part.

  In that case, the difference between the measurement result of the measured optical characteristic and the optical characteristic that should be obtained by the correction result so far is obtained, and the amount of difference from the actual one is calculated (j).

  Specifically, various aberrations such as the above-mentioned field curvature and scanning line curvature are compared, and in particular, in order to correct a partially different part, the sensitivity to various aberrations is calculated for each image height (k), Based on this, partial correction is performed.

  First, a partial curvature for removing residual aberrations is calculated from the sensitivity described above so as to match the measured optical performance, and is polynomialized as described above (l).

Then, the polynomial representing the obtained partial curvature and the polynomial obtained in (f) to (h) are combined, and an approximate polynomial representing this as a single polynomial is created and modeled (m). (End of redesign process)
The correction shape for the current state is calculated from the polynomial thus obtained (n), the specular piece is corrected based on the result (o), and the main forming (p) is performed. (End of mirror surface correction process and main molding process)
The optical performance is evaluated using the optical element molded with the corrected shape obtained as described above, and the shape is measured in this step. Try again.

  As described above, according to the method for manufacturing an optical element of the present invention, since the number of repetitions is initially determined in consideration of the amount of release, there is an effect that the number of repetitions can be smaller than the number of repetitions by the conventional method. .

[About optical design]
Each parameter of the scanning optical system in the optical design is determined by optimizing a plurality of optical characteristics within an allowable range by optical simulation.

  When an optical resin is used as the material of the optical element, an aspherical surface is often used because of the degree of freedom of shape by using injection molding, and it is optimal to obtain good imaging performance for main scanning and sub scanning, respectively. Shape is taken.

  Needless to say, the shape may be a shape in which main scanning and sub-scanning are independent, or may be a sub-scanning shape associated with main scanning.

  In addition, considering the actual arrangement of the optical device used, the optical element is provided with a reference area used for positioning in the apparatus, for example, outside the area having optical performance. May require external dimensions including.

  In this case, it is a matter of course that the outer dimensions are taken into consideration up to an area that does not require imaging performance, but the area used as a mirror piece is an effective area related to imaging, and the effective area that is a curved surface and other planes. In order to smoothly tie the region constituted by the above, a portion that is shaped as a smooth mirror surface is provided outside the main scanning but not involved in the image formation.

  In other words, this data is also prepared as data to be prepared as a design value, and consideration is given so as not to have a step or bending point in the middle of the surface that adversely affects the optical performance.

[About mirror face piece creation]
Conventionally, a method has been used in which temporary molding is first performed using the above-described design values, and the shrinkage and displacement of the optical element are measured and the results are fed back. However, this method inevitably requires temporary molding once. As a result, the number of corrections increases accordingly.

  In the present invention, as shown in FIG. 1, this temporary molding is not performed, and the initial molding is performed based on the result of the mold release amount simulation in which the expected amount of deviation is expected in advance. Can be created by number of times.

  Here, the processes from optical design to initial molding will be described in detail.

  FIG. 4 is a flowchart showing in detail the steps from optical design to initial molding.

From the shape data of the optical element given by the optical design (a), conditions for stable molding described later are set (b-1).
(End of molding condition determination process)
This improves the accuracy of the finished product by giving correction values that predict the shape of the optical element and the resin temperature, injection pressure, temperature distribution of the mold, etc. The molding is performed with a stable quality free from defects such as internal distortion and sink, and not only the shape change of the optical element but also the refractive index distribution inside the optical element is taken into consideration.

Next, based on these setting conditions, the difference between the shape of the optical element based on the optical design value and the shape predicted when actually injection molded, that is, the mold release amount is obtained by simulation, and the mirror surface produced as the shape correction value It is included in advance in the processing value of the piece (b-2).
(End of mold release simulation process)
Then, a mirror surface piece is produced by this mirror surface piece processing value (c), and initial molding (d) is performed using the produced mirror surface piece.
(End of mirror face piece manufacturing process and molding process)
As described above, since the surface shape data for initial forming according to the present proposal is data reflecting conditions at the time of actual forming, it is possible to manufacture an optical element with a small error at the time of the first forming. .

[Measurement of optical properties]
An optical scanning device of the same condition that is actually used is created using the created optical element, and the depth in the optical axis direction is, for example, field curvature and scanning line bending at a plurality of image heights and less than a certain light beam diameter. The width is measured to obtain distribution data of main scanning field curvature, sub-scanning field curvature, and scanning line curvature for each image height.

  Furthermore, perform the above measurements on multiple molded product samples, evaluate the deviation and variation of each optical measurement, and if the variation component deviates from the tolerance, go back to the initial molding process and optimize the molding conditions. I do.

  When the variation is smaller than the tolerance, the relationship between the image height and each optical characteristic is summarized from the measurement data, and whether or not correction is necessary is determined based on the flow of FIG.

[About redesign]
When it is determined that redesign is necessary from the obtained data, redesign is performed to calculate the correction amount. At this time, which of the various aberrations is used as a material for determining that the redesign has improved. The target depends on the nature of the optical scanning device using the optical element or the image forming apparatus using the optical scanning device.

  For example, if the image forming apparatus using an optical element is a color printer that forms a color image by superimposing images from a plurality of optical scanning devices, a scanning line curve is used to suppress color misregistration that is important when superimposing a plurality of light beams. In the case of a high-definition monochrome machine, the curvature of field and the uniformity of minute light beam diameter and magnification are required to obtain a uniform density.

  As described above, various aberrations such as field curvature, scanning line curvature, magnification error, fθ characteristic, and beam diameter are identified as necessary, and each optical element is redesigned so that these are within the allowable range required for the apparatus. Do.

[About correction of specular piece]
In the correction to the specular frame, only the necessary specular frame is corrected based on the correction value for each surface.

  Actually, a mirror piece is created based on a new design shape obtained by adding the change amount of the optical performance surface at the time of redesign to the original design shape.

  Basically, the correction amount required for each surface is calculated and each surface is corrected, but the evaluation after applying the correction has a few points, but there are points to be corrected across multiple surfaces. Then, it is examined whether the same correction effect can be obtained by correcting the number of faces less than the number of faces.

  If possible, the number of surfaces to be actually corrected can be reduced, so that production in a shorter time is possible.

[About this molding]
Using the corrected specular piece, the main molding is performed under the same conditions as the initial molding to create an optical element.

  As a result of measuring the optical characteristics described above using the molded product created by the above-mentioned main molding, if this does not satisfy certain conditions, the process from redesign to main molding is repeated until it meets the tolerance. .

  The flow in the case of repeatedly measuring the optical characteristics, correcting the shape, and correcting the specular piece is as shown in FIG.

[Details of optical measurement]
Next, a method for measuring optical characteristics will be specifically described with reference to FIG.

  FIG. 2 is a layout diagram of measuring tools used when measuring optical characteristics in the optical characteristic measuring step.

  The optical elements 10a and 10b created in the initial molding process described above are incorporated into the optical scanning apparatus 10 that is actually used.

  Note that the optical scanning device 10 may use jigs arranged with the same settings.

  In this case, since the same performance as the optical scanning device to be actually incorporated is required, the seating surface on which the optical element is placed must be configured with high accuracy.

  The measuring tool has a y-stage 12 movable in the main scanning direction in the vicinity of the image plane of the optical scanning device, and a spot measuring device 16 disposed on the y-axis stage, and is movable on the spot measuring device 16 in the sub-scanning direction. The z-axis stage 13 is arranged on the z-axis stage by an x-axis stage 14 which is movable in the optical axis direction, on which an objective lens and a camera 15 comprising a CCD camera are mounted, and each stage is emitted by a computer (not shown). It moves by pulse control.

  Here, the optical axis direction is the x direction, the main scanning direction is the y direction, and the sub scanning direction is the z direction.

  As a measurement procedure, first, a target plate with a cross (not shown) arranged at an image plane position (focus position) in the design of the optical scanning device is arranged, and this is observed with the camera 15.

  The center of the cross of the target plate represents the position where main scanning and sub-scanning intersect on the optical axis, and this is the reference for all positions.

  The target plate may be set at an arbitrary image height with respect to the optical axis of the optical scanning device, not on the optical axis, for convenience of arrangement.

  When the reference is completed, the spot measuring device 16 is moved to the measurement main scanning image height, the light source of the optical scanning device is turned on, and the reflection angle of the polygon motor is adjusted so that the light beam enters the camera 15. The light beam diameter in each scanning direction is measured, and at the same time, the light beam center position is acquired.

  At this time, the height of the z-axis stage is also adjusted by moving the z-axis stage as appropriate so that the light beam enters the approximate center of the camera 15.

  Next, while moving the x-axis stage back and forth, the light beam diameter and position are acquired at several locations before and after the image plane, and the position of the x-axis stage and each light beam diameter are recorded.

  By repeating this operation at a plurality of main scanning image heights, the amount of movement of the x-axis stage and the distribution of the respective light beam diameters at each image height are obtained.

  Here, measurement of the focus shift (deviation from the design image plane in the optical axis direction) will be described with reference to FIG.

  FIG. 3 shows a graph (v) plotting each x direction (position in the optical axis direction) and the light beam diameter when the light beam diameter is measured while moving the camera 15 in the optical axis direction at a certain image height. .

  From the light beam diameter def graph (v), a range that is equal to or smaller than the allowable upper limit value s of the light beam diameter is calculated.

  This means that at each measured image height, there are two positions, the front image plane end a and the rear image plane end b, before and after the position where the light beam diameter becomes the minimum value, and the range in the optical axis direction is calculated. Is.

  Of course, if the minimum value is larger than the standard value, the required performance cannot be obtained.

  An intermediate point (c) is calculated from the two positions thus obtained, and this is set as the focus position of the image height.

  The position where the beam diameter is the smallest is not chosen here, as shown below, when it is actually used in the device, it is better to set the focus at the center of the range where it is less than the specified value and there is less error. It is easy to get.

  For example, if the distribution represented by each x-direction position and the beam diameter is taken, the distribution before and after the position where the beam diameter is minimum may not be symmetrical.

  In this state, for example, when the optical scanning device is incorporated in the main body of the image forming apparatus or the like, the condensing point of the light beam emitted from the optical scanning device, that is, the position where the light beam diameter is minimum is connected to the ideal image plane. Even if an image is formed, the light collection position may be before or after the surface to be scanned on the image forming medium due to an assembly error with an image forming medium such as a drum that forms an image. Performance can be obtained without problems on one side before and after, but on the other side there is a high possibility that the performance will deteriorate immediately (the light beam diameter increases), and it becomes necessary to tighten the accuracy in assembly.

  By setting the image plane at an intermediate point that is not the minimum value but below the specified value, the permissible range can be set equally for both the front and rear, and the performance tends to be stable.

  When measuring the beam diameter, the beam diameters in the main scanning direction and the sub-scanning direction are measured respectively, but the beam diameter is defined by the maximum diameter in the main scanning direction and the sub-scanning direction, which is often used so far. If, for example, the imaging state in the sub-scanning direction is not very good (the light beam diameter is large), the light beam diameter measurement value in the main scanning direction is affected, and the light beam diameter may not be measured correctly.

  If such a phenomenon occurs, the main scanning and sub-scanning influence each other, and the correct imaging position may not be measured, and a position shifted back and forth may be recognized as the imaging position. It will be a hindrance.

  Therefore, in the proposed optical characteristic measurement process, LSF (Line Split Function) is used for measurement.

  Since LSF performs measurement on each line in which main scanning and sub-scanning are independent, it is possible to eliminate the influence of each other and to measure the light collection position with high accuracy.

(Embodiment 2)
The manufacturing method used as the second embodiment will be described below.

  In the above-described release amount simulation, each predicted parameter is prepared. However, in this embodiment, the simulation is performed based on molding conditions of other optical elements having similar molding conditions.

  For example, when an optical scanning device manufactured so far is to be newly manufactured with a configuration that is reduced as it is, the optical element to be used has a proportional shape that is also reduced as it is.

  At this time, when producing the mirror piece, simulation is performed by predicting the mold release amount when the shape is reduced based on the molding conditions of the optical element so far.

  That is, in this embodiment, based on the molding conditions of other similar optical elements such as shape and accuracy, the parameters of the optical element to be manufactured are set and included in the optical design value, and the mold release amount simulation is performed. Then, the machining value of the mirror piece is calculated and molding is performed.

  If necessary, the parameters used in the mold release amount simulation of the first embodiment and the method of performing the simulation calculation from the molding conditions of the similar optical element of the present embodiment may be mixed to create a mirror surface piece processing value. .

It is a flowchart which shows the manufacturing method of the optical element by Embodiment 1 of this proposal. It is an arrangement plan of measuring tools used for measurement of an optical characteristic measurement process. It is the figure which showed the concept which calculates a focus position by distribution of a light beam diameter. It is the flowchart which showed the process from optical design of this proposal to mirror surface piece preparation and initial shaping. It is the flowchart which showed the manufacturing process of the conventional optical element.

Explanation of symbols

10 Optical scanning device 10a, 10b Optical element

Claims (12)

A method for producing an optical element from an optical resin, a molding condition determining step for setting conditions under which stable molding can be performed from a shape based on optical design values,
A mold release amount simulation step for calculating and predicting a mold release amount according to the shape and molding conditions of the optical element,
A method of manufacturing an optical element, comprising: a specular piece manufacturing step of manufacturing a specular piece based on the simulation result; and a forming step of forming using the specular piece. An initial molding step of molding an optical element by the method according to claim 1;
An optical performance measuring step for measuring optical characteristics of the optical element;
A redesign step for correcting the surface shape in order to obtain a target optical performance from the optical performance measured in the optical characteristic measurement step;
A specular piece correction step for correcting and correcting a specular piece based on the correction value obtained in the redesign step, and a main forming step for re-forming with the corrected specular piece. A method for manufacturing an optical element.   The mold release amount simulation step calculates a mold release prediction amount obtained by simulation calculation including at least one of parameters of a resin temperature at the time of molding, an injection pressure, and a temperature distribution of the mold. A method for producing an optical element according to 1.   2. The method of manufacturing an optical element according to claim 1, wherein the mold release amount simulation step calculates a mold release predicted amount by performing simulation calculation based on molding conditions of an optical element having a similar shape.   The specular frame correction step is repeatedly performed from the optical property measurement step so that the measurement value obtained by the optical performance measurement step or the optical performance obtained by optical simulation based on the measurement value becomes a desired value. The manufacturing method of the optical element of Claim 2. The optical performance measurement step is a shape measurement including a mirror shape of the molded optical element,
The method of manufacturing an optical element according to claim 2, further comprising: measuring an imaging state of a light beam by the optical element.   The optical characteristic measurement step obtains a focus position in a main scanning direction of a light beam at a plurality of main scanning image heights by the optical element with respect to a specified image plane in the measurement, and a deviation amount in the optical axis direction with respect to the specified image plane. The method for manufacturing an optical element according to claim 2, wherein:   The optical characteristic measuring step obtains a focus position in a sub-scanning direction of a light beam at a plurality of main scanning image heights by the optical element with respect to a prescribed image plane in the measurement, and in the optical axis direction with respect to the prescribed image plane. The method of manufacturing an optical element according to claim 2, wherein a deviation amount is obtained.   The focus position is determined by measuring a plurality of beam diameters before and after the optical axis direction in the vicinity of the prescribed image plane, and at two positions where the beam diameter distribution is less than or equal to a predetermined beam diameter from the obtained beam diameter distribution. 9. The method for manufacturing an optical element according to claim 7, wherein the two intermediate points are obtained as focus positions for main scanning and sub-scanning.   In the redesign step, the mirror surface shape error obtained in the optical performance measurement step and the optical performance obtained from the measurement result of the imaging state of the light beam by the optical element are combined, and the optical performance is a desired performance. The method of manufacturing an optical element according to claim 2, wherein a shape correction value for the shape error is calculated.   3. The optical system according to claim 2, wherein, in the redesign step, correction is performed for any one or more of field curvature, scanning line curvature, magnification error, fθ characteristic, and beam diameter as optical performance. Device manufacturing method.   An optical element for an optical scanning device manufactured using the manufacturing method according to claim 1.

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