Erect imaging array element and optical unit for exposure having the same

Abstract

To provide an erect imaging array element that can reduce chromatic aberration.SOLUTION: An erect imaging array element has a plurality of transmissive optical elements each including a first optical surface and a second optical surface having a positive refractive power. The plurality of transmissive optical elements are arranged in array. At least one of the first optical surface and the second optical surface is a distribution-controlled diffraction surface. When the Abbe number of the plurality of transmissive optical elements is defined as νd, the conditional expression of |1 / νd|≤0.280 is satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an erect imaging array element and an exposure optical unit having the same. [Background technology]

[0002] BACKGROUND ART Conventionally, a lens array configured by arranging a plurality of small diameter lenses is known (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-130804 Summary of the Invention [Problem to be solved by the invention]

[0004] Figure 10 shows the emission spectrum of a typical LED. Because the lens array has an Abbe number of approximately 10 to 20, the refractive index varies depending on the wavelength of the incident light. This results in wavelength dispersion, where the refractive index is high on the side where the wavelength of the incident light is short and low on the side where the wavelength is long. In other words, when light with a wide spectral width that includes light of various wavelengths enters the lens array, the focal length shifts due to the difference in refractive index caused by wavelength dispersion.

[0005] An object of the present invention is to provide an erect imaging array element capable of reducing chromatic aberration. [Means for solving the problem]

[0006] An erect image-forming array element according to one aspect of the present invention has a plurality of transmissive optical elements each having a first optical surface and a second optical surface, the first optical surface and the second optical surface having a positive refractive power, the plurality of transmissive optical elements being arranged in an array, and at least one of the first optical surface and the second optical surface being a dispersion-controlled diffractive surface, and when the Abbe number of each of the plurality of transmissive optical elements is νd, |1 / νd|≦0.280 The present invention is characterized in that the following conditional expression is satisfied: [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an erect imaging array element capable of reducing chromatic aberration. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an exposure apparatus according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the transmissive optical element of the first embodiment. [Figure 3] FIG. 1 is a perspective view of an exposure apparatus according to a first embodiment. [Figure 4] FIG. 2 is a diagram showing a wafer for producing a lens according to the first embodiment. [Figure 5] 4A to 4C are aberration diagrams of the erect imaging array element of Example 1. [Figure 6] FIG. 4 is a diagram showing the amount of focus change in the first embodiment. [Figure 7] FIG. 10 is a diagram showing the amount of focus change in the second embodiment. [Figure 8] FIG. 11 is a diagram showing the amount of focus change in the third embodiment. [Figure 9] FIG. 10 is a diagram showing the amount of focus change in the fourth embodiment. [Figure 10] FIG. 1 is a diagram showing the emission spectrum of a typical LED (conventional example). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals are used to designate the same components, and redundant explanations will be omitted.

[0010] Image reading devices (image forming devices) that print images by developing a toner image by attaching toner to an electrostatic latent image formed on the surface of a photosensitive drum using light from an exposure device (exposure optical unit) are widely used. For example, an LED head that utilizes light emitted from LEDs (Light Emitting Diodes) is used as the exposure device. The LED head has a substrate on which an LED array, in which multiple LEDs are arranged linearly, is mounted, and a lens unit in which multiple lenses are aligned to focus the light emitted from each LED. The light emitted from the LED array passes through the lens unit and is converged, and is then exposed to the surface of a photosensitive drum located at the imaging position of the lens unit, thereby forming an electrostatic latent image.

[0011] In each embodiment, the configuration of the lens unit will be described. [Example]

[0012] 1 is a schematic diagram of an exposure apparatus according to this embodiment. The exposure apparatus has a light source 1 and an erect imaging array element 50, which is a lens unit.

[0013] The light source 1 is configured to include an OLED (organic light emitting element). In this embodiment, the light source 1 is configured with a plurality of 20 μm light emitting points arranged in an array. A central light beam 1a and a peripheral light beam 1b of the light beam emitted from the light source 1 pass through a plurality of lenses (three in this embodiment) and are condensed onto an image plane 2 (the surface of the photosensitive drum 20).

[0014] The erect imaging array element 50 has a first lens array 3 and a second lens array 4 arranged in this order from the object side (the side of the light source 1) to the image side (the side of the image plane 2). As will be described later, the two lens arrays are configured by cementing a plurality of lenses. The first lens array 3 has a substrate 30. In this embodiment, an optical surface (first optical surface) 31 is provided on the object-side surface of the substrate 30, which is the incident surface through which light from the light source 1 is incident, and has convex power (positive refractive power). The second lens array 4 has a substrate 40. In this embodiment, an optical surface (second optical surface) 41 is provided on the image-side surface of the substrate 40, which is the exit surface through which light from the light source 1 exits, and has convex power (positive refractive power). The first lens array 3 and the second lens array 4 are bonded to a flat glass 32 with an adhesive and integrated via the bonding surface. That is, the optical surfaces 31 and 41 are provided on an integrally constructed element. Furthermore, the first lens array 3 and the second lens array 4 have the same shape. That is, the optical surfaces 31 and 41 have the same shape, so that the erect imaging array element 50 can be easily manufactured.

[0015] In this embodiment, the substrate 30 is a roughly rectangular parallelepiped member made of glass and 0.775 mm thick. The optical surface 31 is a dispersion-controlled diffractive surface formed by an etching process and composed of a plurality of minute cylindrical pillars with a height of 1000 nm and a diameter of 70 to 300 nm. The substrate 40 is a roughly rectangular parallelepiped member made of glass and 0.775 mm thick. The optical surface 41 is a dispersion-controlled diffractive surface formed by an etching process and composed of minute cylindrical pillars with a height of 1000 nm and a diameter of 70 to 300 nm. The flat glass 32 is made of Bk7 (borosilicate crown glass). At least one surface of the flat glass 32, facing the direction where the two lens arrays are joined, is coated with a light-blocking paint. This prevents light beams from entering adjacent lenses. Each lens constituting the lens array adds a continuous phase to the wavefront of the incident light beam, thereby bending the light's traveling direction.

[0016] In this embodiment, both optical surfaces 31 and 41 are dispersion-controlled diffractive surfaces, but one may be a dispersion-controlled diffractive surface and the other a refractive surface.

[0017] In addition, in this embodiment, optical surface 31 is provided on the object-side surface of substrate portion 30, but it may also be provided on the image-side surface, and optical surface 41 is provided on the image-side surface of substrate portion 40 in this embodiment, but it may also be provided on the object-side surface.

[0018] FIG. 2 is a cross-sectional view of the transmissive optical element of this embodiment. A plurality of transmissive optical elements are arranged in an array to form an erect imaging array element 50. In this embodiment, as shown in FIG. 3, the erect imaging array element 50 is a two-dimensional array. The first lens 101 is one of the lenses that form the first lens array 3. The second lens 103 is one of the lenses that form the second lens array 4. The first lens 101 and the second lens 103 are bonded to a flat glass 102 with an adhesive and are integrated via the bonding surface.

[0019] Light from the light source 1 is incident on the optical surface 101a of the first lens 101. The optical surface 101a is part of the optical surface 31. As will be described later, the phase coefficient of the optical surface 31 is determined so that an image is formed inside the flat glass 102. The light beam that has formed an image inside the flat glass 102 is incident on the second lens 103, passes through the optical surface 103a of the second lens 103, and is condensed onto the image plane 104. As a result, the object point is imaged as an erect image on the image plane 104. The optical surface 103a is part of the optical surface 41, and the image plane 104 is part of the image plane 2.

[0020] Table 1 shows the optical parameters of this embodiment. * in Table 1 indicates surfaces whose structure is determined by the phase function. In this embodiment, the structure of optical surfaces 31 and 41 is determined by the phase function expressed by the following equation (1). In this embodiment, the phase function is determined by an eighth-order function in the radial direction from the center of the optical axis. Table 2 shows each phase coefficient of the phase function.

[0021] [Table 1]

[0022] [Table 2]

[0023]

number

[0024] (1) FIG. 4 is a diagram showing a wafer (substrate) 200 for producing lenses 201 that constitute the lens array of this embodiment. The wafer 200 is made of a glass base material. A plurality of cylindrical pillars on the order of nanometers are formed on the surface of the lens 201. In this embodiment, the lens 201 can be produced using a high-precision semiconductor production process. That is, a fine shape on the order of nanometers is produced on the wafer 200, and a high-precision cutting and bonding process is utilized to produce a high-precision erect imaging array element 50.

[0025] FIG. 5 shows aberration diagrams of the erect imaging array element 50 of this embodiment. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism in the sagittal image plane, and M shows the amount of astigmatism in the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (°). In this embodiment, the provision of a dispersion-controlled diffractive surface enables aberration correction equivalent to that of an aspherical lens. Therefore, spherical aberration and astigmatism are corrected.

[0026] In this embodiment, the light source 1 irradiates visible light onto the erect imaging array element 50. In this embodiment, the visible light irradiated is light with a wavelength of 500 nm to 700 nm. The design wavelength is 600 nm. As described above, the erect imaging array element 50 has a dispersion-controlled diffractive surface. In this embodiment, the dispersion-controlled diffractive surface is designed so that the phase function does not change even when light with a wavelength of 590 nm to 610 nm is incident, compared to a design wavelength of 600 nm. Specifically, the phase delay amount of the meta-atom is calculated for each wavelength, and the meta-atom is arranged to control the dispersion of the lens.

[0027] It is preferable that the transmitting optical element satisfies the following conditional expression (1).

[0028] |1 / νd|≦0.280 (1) Here, νd is the Abbe number of the transmitting optical element.

[0029] By satisfying conditional expression (1), it is possible to reduce the change in refractive index (dispersion) with respect to the change in wavelength of light from the light source 1. Specifically, even if the wavelength of light from the light source 1 changes by 10 nm (for example, from 600 nm to 610 nm), it is possible to suppress the change in the focal position. In this embodiment, the Abbe number νd is zero.

[0030] It is preferable that the numerical range of conditional expression (1) be the numerical range of conditional expression (1a) below.

[0031] |1 / νd|≦0.02 (1a) It is more preferable that the numerical range of conditional expression (1) be the numerical range of the following conditional expression (1b).

[0032] |1 / νd|≦0.0125 (1b) 6 is a diagram showing the amount of focus change (amount of chromatic aberration, amount of focus shift) when the wavelength of light from light source 1 of this embodiment changes by 10 nm (when changing from 600 nm to 610 nm). The horizontal axis shows the position (image height) of the light-emitting point relative to the optical axis of erect imaging array element 50, and the vertical axis shows the amount of focus change when the wavelength of light from light source 1 changes by 10 nm. As shown in FIG. 6, with the configuration of this embodiment, regardless of the position of the light-emitting point, the amount of focus change when the wavelength of light from light source 1 changes by 10 nm is within the range of -0.02 mm to 0.02 mm, which is sufficiently suppressed.

[0033] Moreover, it is preferable that the erect imaging array element 50 satisfies the following conditional expression (2).

[0034] |Φ1 / νd1+Φ2 / νd1|≦0.03 (2) Here, Φ1 is the power of the optical surface 31. Φ2 is the power of the optical surface 41. νd1 is the dispersion characteristic of the optical surface 31. νd2 is the dispersion characteristic of the optical surface 41.

[0035] In this embodiment, the powers Φ1 and Φ2 are positive, and the values ​​1 / νd1 and 1 / νd2 are zero. Note that "zero" does not only mean strictly zero, but also includes substantially zero (nearly zero). Specifically, the powers Φ1 and Φ2 are 0.89, and the values ​​1 / νd1 and 1 / νd2 are zero, so conditional expression (2) is satisfied.

[0036] It is preferable that the numerical range of conditional expression (2) be the numerical range of the following conditional expression (2a).

[0037] |Φ1 / νd1+Φ2 / νd1|≦0.02 (2a) It is more preferable that the numerical range of conditional expression (2) be the numerical range of the following conditional expression (2b).

[0038] |Φ1 / νd1+Φ2 / νd1|≦0.01 (2b) As described above, the configuration of this embodiment can provide an erect imaging array element 50 capable of reducing chromatic aberration. [Example]

[0039] This embodiment differs from the first embodiment in that the value 1 / νd is set to −0.01. The other configurations are the same as those of the first embodiment.

[0040] The optical parameters of this example are shown in Table 3. * in Table 3 indicates a surface whose structure is determined by the phase function. Table 4 shows each phase coefficient of the phase function.

[0041] In this embodiment, the dispersion-controlled diffractive surface is designed so that the phase function does not change even when light with a wavelength of 590 nm to 610 nm is incident, relative to a design wavelength of 600 nm. In this embodiment, the value 1 / νd is −0.01, which satisfies conditional expression (1). This makes it possible to suppress changes in the focal position even when the wavelength of light from light source 1 changes by 10 nm (for example, from 600 nm to 610 nm).

[0042] 7 is a diagram showing the amount of focus change when the wavelength of light from light source 1 in this embodiment changes by 10 nm (from 600 nm to 610 nm). The horizontal axis shows the position (image height) of the light-emitting point relative to the optical axis of the erect imaging array element 50, and the vertical axis shows the amount of focus change when the wavelength of light from light source 1 changes by 10 nm. As shown in FIG. 7, regardless of the position of the light-emitting point, the amount of focus change when the wavelength of light from light source 1 changes by 10 nm is within the range of -0.02 mm to 0.02 mm, which is sufficiently suppressed.

[0043] [Table 3]

[0044] [Table 4]

[0045] In this embodiment, the powers Φ1 and Φ2 are 0.89, and the values ​​1 / νd1 and 1 / νd2 are −0.01 with the same sign, which satisfies the conditional expression (2).

[0046] As described above, the configuration of this embodiment can provide an erect imaging array element 50 that can reduce chromatic aberration. Furthermore, by setting the value 1 / νd to −0.01, the fine shape of the dispersion-controlled diffractive surface can be simplified, making it easier to manufacture. [Example]

[0047] This embodiment differs from the first embodiment in that the value 1 / νd is set to 0.01 and the value 1 / νd2 is set to −0.09. The other configurations are the same as those of the first embodiment.

[0048] Table 5 shows the optical parameters of this example. * in Table 5 indicates a surface whose structure is determined by the phase function. Table 6 shows each phase coefficient of the phase function.

[0049] In this embodiment, the dispersion-controlled diffractive surface is designed so that the phase function does not change even when light with a wavelength of 590 nm to 610 nm is incident, relative to a design wavelength of 600 nm. In this embodiment, the value 1 / νd is 0.01, which satisfies conditional expression (1). This makes it possible to suppress changes in the focal position even when the wavelength of light from light source 1 changes by 10 nm (for example, from 600 nm to 610 nm).

[0050] 8 is a diagram showing the amount of focus change when the wavelength of light from light source 1 in this embodiment changes by 10 nm (when changing from 600 nm to 610 nm). The horizontal axis shows the position (image height) of the light-emitting point relative to the optical axis of the erect imaging array element 50, and the vertical axis shows the amount of focus change when the wavelength of light from light source 1 changes by 10 nm. As shown in FIG. 8, regardless of the position of the light-emitting point, the amount of focus change when the wavelength of light from light source 1 changes by 10 nm is within the range of -0.02 mm to 0.02 mm, which is sufficiently suppressed.

[0051] [Table 5]

[0052] [Table 6]

[0053] In this embodiment, specifically, the powers Φ1 and Φ2 are 0.89, the value 1 / νd1 is 0.01, and the value 1 / νd2 is −0.009, which satisfies the conditional expression (2).

[0054] As described above, the configuration of this embodiment can provide an erect imaging array element 50 that can reduce chromatic aberration. Furthermore, by setting the value 1 / νd1 to 0.01 and the value 1 / νd2 to -0.009, the fine shape of the dispersion-controlled diffractive surface can be simplified, making it easier to manufacture. [Example]

[0055] This embodiment differs from the first embodiment in that the values ​​1 / νd and 1 / νd2 are set to 0.011. The other configurations are the same as those of the first embodiment.

[0056] Table 7 shows the optical parameters of this example. * in Table 7 indicates a surface whose structure is determined by the phase function. Table 8 shows each phase coefficient of the phase function.

[0057] In this embodiment, the dispersion-controlled diffractive surface is designed so that the phase function does not change even when light with a wavelength of 590 nm to 610 nm is incident, relative to a design wavelength of 600 nm. In this embodiment, the value 1 / νd is 0.011, which satisfies conditional expression (1). This makes it possible to suppress changes in the focal position even when the wavelength of light from light source 1 changes by 10 nm (for example, from 600 nm to 610 nm).

[0058] 9 is a diagram showing the amount of focus change when the wavelength of light from light source 1 in this embodiment changes by 10 nm (from 600 nm to 610 nm). The horizontal axis shows the position (image height) of the light-emitting point relative to the optical axis of the erect imaging array element 50, and the vertical axis shows the amount of focus change when the wavelength of light from light source 1 changes by 10 nm. As shown in FIG. 9, regardless of the position of the light-emitting point, the amount of focus change when the wavelength of light from light source 1 changes by 10 nm is within the range of -0.02 mm to 0.02 mm, which is sufficiently suppressed.

[0059] [Table 7]

[0060] [Table 8]

[0061] In this embodiment, the powers Φ1 and Φ2 are 0.89, and the values ​​1 / νd1 and 1 / νd2 are 0.011 with the same sign, which satisfies the conditional expression (2).

[0062] As described above, the configuration of this embodiment can provide an erect imaging array element 50 that can reduce chromatic aberration. Furthermore, by setting the values ​​1 / νd and 1 / νd2 to 0.011, the fine shape of the dispersion-controlled diffractive surface can be simplified, making it easier to manufacture.

[0063] The disclosure of this embodiment includes the following configuration. (Configuration 1) a plurality of transmissive optical elements each having a first optical surface and a second optical surface, the first optical surface and the second optical surface having a positive refractive power; The plurality of transmissive optical elements are arranged in an array, at least one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface; When the Abbe number of each of the plurality of transmitting optical elements is νd, |1 / νd|≦0.280 1. An erect imaging array element characterized by satisfying the following conditional expression: (Configuration 2) 2. The erect imaging array element according to configuration 1, wherein the first optical surface and the second optical surface are dispersion-controlled diffractive surfaces. (Configuration 3) When the power of the first optical surface is Φ1, the power of the second optical surface is Φ2, the dispersion characteristic of the first optical surface is νd1, and the dispersion characteristic of the second optical surface is νd2, |Φ1 / νd1+Φ2 / νd1|≦0.03 3. The erect imaging array element according to configuration 2, wherein the following condition is satisfied: (Configuration 4) the power of the first optical surface and the power of the second optical surface are positive; 4. The erect imaging array element according to configuration 3, wherein the dispersion characteristics of the first optical surface and the dispersion characteristics of the second optical surface have values ​​of the same sign. (Configuration 5) the power of the first optical surface and the power of the second optical surface are positive; 4. The erect imaging array element according to configuration 3, wherein the values ​​1 / νd1 and 1 / νd2 are zero. (Configuration 6) 4. The erect imaging array element according to configuration 3, wherein the first optical surface and the second optical surface have the same shape. (Configuration 7) one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface; 2. The erect imaging array element according to configuration 1, wherein the other of the first optical surface and the second optical surface is a refractive surface. (Configuration 8) The erect imaging array element according to any one of configurations 1 to 7, wherein the first optical surface and the second optical surface are provided on an integrally configured element. (Configuration 9) 8. The erect imaging array element according to any one of configurations 1 to 7, which is a two-dimensional array. (Configuration 10) a plurality of transmissive optical elements each having a first optical surface and a second optical surface, the first optical surface and the second optical surface having a positive refractive power; The plurality of transmissive optical elements are arranged in an array, 1. An erect imaging array element, wherein at least one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface. (Configuration 11) an erect imaging array element according to any one of configurations 1 to 10; a light source for irradiating the erect imaging array element with light, (Configuration 12) 12. The exposure optical unit according to claim 11, wherein the light source includes an organic EL element. (Configuration 13) 13. The exposure optical unit according to configuration 11 or 12, wherein the light source irradiates the erect imaging array element with visible light. (Configuration 14) the first optical surface is an incident surface onto which light from the light source is incident, 14. The exposure optical unit according to any one of configurations 11 to 13, wherein the second optical surface is an exit surface through which light from the light source exits.

[0064] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0065] 3 First lens array 4 Second lens array

Claims

1. a plurality of transmissive optical elements each having a first optical surface and a second optical surface, the first optical surface and the second optical surface having a positive refractive power; The plurality of transmissive optical elements are arranged in an array, at least one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface; When the Abbe number of each of the plurality of transmitting optical elements is νd, |1 / νd|≦0.280 1. An erect imaging array element characterized by satisfying the following conditional expression:

2. 2. The erect imaging array element according to claim 1, wherein the first optical surface and the second optical surface are dispersion-controlled diffractive surfaces.

3. When the power of the first optical surface is Φ1, the power of the second optical surface is Φ2, the dispersion characteristic of the first optical surface is νd1, and the dispersion characteristic of the second optical surface is νd2, |Φ1 / νd1+Φ2 / νd1|≦0.03 3. The erect imaging array element according to claim 2, wherein the following condition is satisfied:

4. the power of the first optical surface and the power of the second optical surface are positive; 4. The erect imaging array element according to claim 3, wherein the dispersion characteristics of the first optical surface and the dispersion characteristics of the second optical surface have values ​​of the same sign.

5. the power of the first optical surface and the power of the second optical surface are positive; 4. The erect imaging array element according to claim 3, wherein the value 1 / νd1 and the value 1 / νd2 are zero.

6. 4. The erect imaging array element according to claim 3, wherein the first optical surface and the second optical surface have the same shape.

7. one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface; 2. The erect imaging array element according to claim 1, wherein the other of the first optical surface and the second optical surface is a refractive surface.

8. 7. The erect imaging array element according to claim 1, wherein the first optical surface and the second optical surface are provided on an integrally constructed element.

9. 7. The erect imaging array element according to claim 1, which is a two-dimensional array.

10. a plurality of transmissive optical elements each having a first optical surface and a second optical surface, the first optical surface and the second optical surface having a positive refractive power; The plurality of transmissive optical elements are arranged in an array, 10. An erect imaging array element, wherein at least one of the first optical surface and the second optical surface is a dispersion-controlled diffractive surface.

11. an erect imaging array element according to claim 1 or 2; a light source for irradiating the erect imaging array element with light,

12. 12. The exposure optical unit according to claim 11, wherein the light source includes an organic EL element.

13. 12. The exposure optical unit according to claim 11, wherein the light source irradiates the erect imaging array element with visible light.

14. the first optical surface is an incident surface onto which light from the light source is incident, 12. The exposure optical unit according to claim 11, wherein the second optical surface is an exit surface through which light from the light source exits.

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