Illumination optical system

Abstract

This illumination optical system comprises, in order from the illumination target side, a first lens having positive refractive power, a second lens having negative refractive power, and a third lens having positive refractive power. When the illumination optical system, being regarded as an imaging optical system with respect to a light flux made incident from the illumination object side, has a combined focal length of f millimeters and a combined refractive power Pt = 1 / f, and when, assuming that the three lenses have first to sixth surfaces from the illumination object side, the fifth surface has a refractive power P5 and the second lens has a central thickness of L2, the following expressions are satisfied. 1.3 < P5 / Pt 0.1 < L2 / f < 0.25

Description

Illumination optical system

[0001] The present invention relates to an illumination optical system used for vehicle headlamps and the like.

[0002] In recent years, an illumination optical system for Adaptive Driving Beam (ADB) light distribution control has been developed in vehicle headlamps (Patent Document 1). In ADB light distribution control, a plurality of LEDs (light-emitting diodes) arranged as light sources are individually controlled according to the situation of other vehicles in front of the vehicle, etc., so that the irradiation target area, irradiation intensity, etc. are controlled. Therefore, in ADB light distribution control, it is required that the irradiation area of each LED can be individually controlled. Therefore, in the illumination optical system, it is necessary to reduce as much as possible the phenomenon of flare, which is the irradiation of an unintended area. Also, the illumination optical system is desirably bright.

[0003] Therefore, in the field of vehicle headlamps and the like, there is a need for an illumination optical system that is bright and has little flare.

[0004] JP 2019-573638 (Patent 002897)

[0005] The technical problem of the present invention is to provide an illumination optical system that is bright and has little flare.

[0006] The illumination optical system of the present invention includes a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power in order from the illumination target side. When the illumination optical system is regarded as an imaging optical system for the light beam incident from the illumination target side, the combined focal length is f millimeters, the combined refractive power is Pt = 1 / f, and each surface of the three lenses is defined as the first to sixth surfaces from the illumination target side. The refractive power of the fifth surface is P5, and the central thickness of the second lens is L2. 1.3 < P5 / Pt 0.1 < L2 / f < 0.25 is satisfied.

[0007] According to the present invention, the coma aberration when the illumination optical system is regarded as an imaging optical system for the light beam incident from the illumination target side is reduced, and the flare of the illumination optical system corresponding to the coma aberration is reduced.

[0008] In the illumination optical system of the first embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the proportion of light rays that reach the image plane among light rays of the light beam that are incident on the illumination object side surface of the first lens at an angle of 25 degrees with respect to the optical axis is in the range of 14% to 20%.

[0009] In the illumination optical system according to the second embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, F<0.7 is satisfied, where F is the F-number.

[0010] The illumination optical system of this embodiment provides sufficient luminous intensity.

[0011] In the illumination optical system according to the third embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination target side, the focal range of axial chromatic aberration of light rays with wavelengths from 0.420 micrometers to 0.680 micrometers based on the d-line (588 nanometers) is defined as c millimeters, and the relationship c / f<0.00292 is satisfied.

[0012] According to the illumination optical system of this embodiment, chromatic dispersion on the illumination surface is reduced.

[0013] In the illumination optical system of the fourth embodiment of the present invention, when the illumination optical system is regarded as an imaging optical system for a light beam incident from the illumination object side, the distortion of a light ray incident on the illumination object side surface of the first lens at an angle of 20 degrees with respect to the optical axis is negative, and the absolute value of the distortion is 5% or more.

[0014] The illumination optical system of this embodiment can illuminate a wider range than when there is no distortion.

[0015] In the illumination optical system according to the fifth embodiment of the present invention, the materials of the first lens, the second lens and the third lens are acrylic, polycarbonate and acrylic, respectively.

[0016] In the illumination optical system of this embodiment, acrylic and polycarbonate, which have different refractive indices, are used as materials for the three lenses. This reduces axial chromatic aberration when the illumination optical system is considered as an imaging optical system for a light beam incident from the illumination target side, thereby making it possible to reduce chromatic dispersion on the illumination surface.

[0017] In the illumination optical system according to a third embodiment of the present invention, the first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens.

[0018] 1 is a diagram showing an example of an illumination optical system according to the present invention;

[0023] FIG. 1 is a diagram showing the paths of light rays when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in FIG. 1 at an angle of 25 degrees with the optical axis of the illumination optical system;

[0024] FIG. 1 is a diagram showing the area of ​​surface S1 through which, of the parallel light beams that are incident on surface S1 of the optical system and are parallel to the optical axis, pass without being vignetted and reach a surface that includes point O and is perpendicular to the optical axis;

[0025] FIG. 1 is a diagram showing the area of ​​surface S1 through which, of the parallel light beams that are incident on surface S1 of the optical system and are at an angle of 25 degrees with the optical axis, pass without being vignetted and reach a surface that includes point O and is perpendicular to the optical axis;

[0026] FIG. 1 is a diagram showing the proportion of the parallel light beams that are incident on surface S1 of the optical system and are at an angle of 23 degrees with the optical axis of the illumination optical system, pass without being vignetted and reach a surface that includes point O and is perpendicular to the optical axis;

[0027] 1 shows the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in FIG. 1 , forming an angle of 23 degrees with the optical axis of the illumination optical system. FIG. 2 shows the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system of a comparative example, forming an angle of 23 degrees with the optical axis of the illumination optical system. FIG. 3 shows flare on a plane perpendicular to the z axis caused by a light source placed at a point on the x axis away from point O by a distance between points O and E". FIG. 4 shows the path of a light ray when a parallel light beam is incident on an optical system in which the central thickness of the second lens is changed and the optical system is 4.0 millimeters, forming an angle of 23 degrees with the optical axis.

[0019] 1 is a diagram showing the path of light rays when a parallel light beam making an angle of 23 degrees with respect to the optical axis is incident on an optical system of 5.5 millimeters in which the central thickness of the second lens is changed; FIG. 2 is a diagram showing the path of light rays when a parallel light beam making an angle of 23 degrees with respect to the optical axis is incident on an optical system of 8.5 millimeters in which the central thickness of the second lens is changed; FIG. 3 is a diagram showing the curvature of field when the embodiment is considered to be an imaging optical system; FIG. 4 is a diagram showing distortion when the embodiment is considered to be an imaging optical system; and FIG. 5 is a diagram showing axial chromatic aberration when the embodiment is considered to be an imaging optical system.

[0020] FIG. 1 shows an example of an illumination optical system according to the present invention. The illumination optical system includes a first lens L1, a second lens L2, and a third lens L3, and is configured to irradiate an object with light from a light source having a center at point O. The first lens L1 is closest to the illumination object, and the third lens L3 is closest to the light source. The surfaces of the first lens L1, the second lens L2, and the third lens L3 facing the illumination object are designated S1, S3, and S5, respectively, and the surfaces of the first lens L1, the second lens L2, and the third lens L3 facing the light source are designated S2, S4, and S6. The illumination optical system is disposed so that its optical axis passes through point O. FIG. 1 shows the path of a collimated light beam parallel to the optical axis of the illumination optical system when it is incident on surface S1 from the illumination object side of the illumination optical system.

[0021] Each lens surface is expressed by the following formula: z represents the coordinate of a point on the surface along the optical axis from the vertex of the lens surface. r represents the distance of a point on the surface from the optical axis. c represents the curvature, k represents the Conic constant, and αi represents the aspheric coefficient. The sign of the curvature c is defined as positive when the surface is convex toward the illumination object side, and negative when the surface is concave toward the illumination object side.

[0022] Table 1 shows the shapes, materials, and positions of the lenses in the illumination optical system of the example. The radius of curvature is the reciprocal of the curvature c. The "thickness or distance" in the row S1 indicates the thickness (center thickness) of the first lens L1, and the "thickness or distance" in the row S6 indicates the distance along the optical axis from the surface S6 to the point O at the center of the light source.

[0023] Table 2 shows the values ​​of the aspherical coefficients of each lens surface. The value of any aspherical coefficient not shown in the table is 0.

[0024] In the following, the illumination optical system shown in Figure 1 will be considered as an imaging optical system. As mentioned above, Figure 1 shows the path of light rays when a parallel light beam parallel to the optical axis of the illumination optical system is incident on a surface S1 from the illumination target side. The parallel light beam is focused at point O.

[0025] Figure 2 shows the path of a parallel light beam incident on a surface S1 from the illumination target side of the illumination optical system shown in Figure 1, at an angle of 25 degrees with the optical axis of the illumination optical system. The parallel light beam reaches the vicinity of point E on a plane that includes point O and is perpendicular to the optical axis. Considering the path of the light beam shown in Figures 1 and 2, it is estimated that if a light source such as an LED (light-emitting diode) is placed in a range from point O to points O and E on a plane that includes point O and is perpendicular to the optical axis, it will be possible to illuminate an area that forms an angle of 25 degrees or less with the optical axis from the light source as its center.

[0026] Table 3 shows the refractive power of each lens surface and the composite refractive power of the imaging optical system in this example. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. In Table 3, "ratio" refers to the ratio of the refractive power of each surface to the composite refractive power. The composite focal length of the imaging optical system is 34.697 millimeters. The F-number is 0.65. Generally, an F-number smaller than 0.7 is preferable.

[0027] In this embodiment, the refractive power of the surface S5 is relatively large as shown in Table 3. The reason for making the refractive power of the surface S5 relatively large will be explained below.

[0028] In an illumination optical system, illumination of an unintended area may occur, which is called flare. Flare is a major obstacle in ADB light distribution control, which requires highly accurate determination of the illumination position of each LED. Flare in an illumination optical system corresponds to coma aberration when the illumination optical system is considered as an imaging optical system. In other words, the larger the coma aberration when considered as an imaging optical system, the larger the flare in the illumination optical system. Therefore, to reduce flare in an illumination optical system, it is necessary to reduce the coma aberration when considered as an imaging optical system. One method for reducing coma aberration is to use vignetting to reduce the proportion of rays that reach a plane that includes point O and is perpendicular to the optical axis, among parallel light beams that form a relatively large angle with the optical axis.

[0029] Fig. 3 is a diagram showing the area of ​​surface S1 through which light rays pass that, among the parallel light beams that are incident on surface S1 of the optical system and are parallel to the optical axis, reach a plane that includes point O and is perpendicular to the optical axis without being vignetted. The diagram on the left side of Fig. 3 shows a plan view of surface S1, and the diagram on the right side of Fig. 3 shows the configuration path of the optical system, similar to Fig. 1. According to Fig. 3, light rays that pass through almost the entire area of ​​surface S1 reach a plane that includes point O and is perpendicular to the optical axis without being vignetted. The diagram on the right side of Fig. 3 shows the path of the light rays, similar to Fig. 1.

[0030] Fig. 4 is a diagram showing the area of ​​surface S1 through which light rays pass that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted, out of a bundle of parallel rays that are incident on surface S1 of the optical system and form an angle of 25 degrees with the optical axis. The diagram on the left side of Fig. 4 shows a plan view of surface S1, and the diagram on the right side of Fig. 4 shows the structural path of the optical system, similar to Fig. 2. According to Fig. 4, the area of ​​surface S1 through which light rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted pass is 20 percent or less of the entire area.

[0031] Fig. 5 is a diagram showing the proportion of rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted among a collimated beam of light that is incident on surface S1 of the optical system. The horizontal axis of Fig. 5 represents the angle that the collimated beam makes with the optical axis. The vertical axis of Fig. 5 represents the proportion of rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted. According to Fig. 5, when the angle that the collimated beam makes with the optical axis is 25 degrees, the proportion of rays that reach a plane that includes point O and is perpendicular to the optical axis without being vignetted is approximately 15 percent.

[0032] As shown in FIG. 4, when the angle that the parallel light beam makes with the optical axis is 25 degrees, by decreasing the radius of curvature of surface S5 and increasing its refractive power, a portion of the light rays diverging from surface S4 are more likely to be vignetted, and the proportion of light rays that reach a surface that includes point O and is perpendicular to the optical axis without being vignetted decreases.

[0033] In general, it is preferable that the ratio of the refractive power of surface S5 to the composite refractive power be greater than 1.3.Furthermore, when the angle between the parallel light beam and the optical axis is 25 degrees, the percentage of light rays that reach a surface that includes point O and is perpendicular to the optical axis without being vignetted is preferably in the range of 14% to 20%.

[0034] Table 4 shows the values ​​of each aberration of each surface of the imaging optical system. "Total" is the sum of the aberrations of each surface, and represents the aberration of the entire imaging optical system. According to Table 4, the aberration of surface S5 contributes to reducing the aberration of the entire imaging optical system. Increasing the radius of curvature of surface S5 (reducing the refractive power) tends to increase the aberration of the entire imaging optical system. From this perspective, too, it is preferable that the ratio of the refractive power of surface S5 to the composite refractive power be within the above range.

[0035] Figure 6 shows the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of the illumination optical system shown in Figure 1, forming an angle of 23 degrees with the optical axis of the illumination optical system. The parallel light beam reaches the vicinity of point E' on a plane that includes point O and is perpendicular to the optical axis. In Figure 6, point O is the origin, and the optical axis of the optical system is the z-axis. The x-axis is perpendicular to the plane of the paper on which Figure 6 is drawn.

[0036] FIG. 7 is a diagram showing a flare on a plane perpendicular to the z-axis caused by a light source located at a point on the x-axis separated from point O by a distance between point O and point E'. The light source is, for example, a light-emitting diode. The horizontal axis of FIG. 7 represents the angle between the z-axis and a line projected onto the xz plane of a light ray emitted from the light source. The vertical axis of FIG. 7 represents the angle between the z-axis and a line projected onto the yz plane of a light ray emitted from the light source.

[0037] Another illumination optical system will be considered below as a comparative example.

[0038] Table 5 shows the shapes, materials, and positions of the lenses in the illumination optical system of the comparative example. The "thickness or spatial length" in the row S1 indicates the thickness (center thickness) of the first lens L1, and the "thickness or spatial length" in the row S6 indicates the distance along the optical axis from the surface S6 to the point O at the center of the light source.

[0039] Table 6 shows the aspherical coefficients of each lens surface.

[0040] Table 7 shows the refractive power of each lens surface and the composite refractive power of the imaging optical system of the comparative example. The composite refractive power is the reciprocal of the composite focal length of the imaging optical system. The composite focal length of the imaging optical system is 34.799 millimeters. The F-number is 0.66.

[0041] 8 is a diagram showing the path of a light ray when a parallel light beam is incident on a surface S1 from the illumination target side of an illumination optical system of a comparative example, forming an angle of 23 degrees with the optical axis of the illumination optical system. The parallel light beam reaches the vicinity of point E" on a plane that includes point O and is perpendicular to the optical axis. In FIG. 8, point O is the origin, and the optical axis of the optical system is the z-axis. The x-axis is perpendicular to the plane of the paper on which FIG. 8 is drawn.

[0042] FIG. 9 is a diagram showing flare on a plane perpendicular to the z-axis caused by a light source placed at a point on the x-axis away from point O by a distance between point O and point E″. The light source is, for example, a light-emitting diode. The horizontal axis of FIG. 9 represents the angle between the z-axis and a line obtained by projecting the light beam emitted from the light source onto the xz plane. The vertical axis of FIG. 9 represents the angle between the z-axis and a line obtained by projecting the light beam emitted from the light source onto the yz plane.

[0043] Comparing Fig. 7 , which shows the flare of the illumination optical system of the example, with Fig. 9 , which shows the flare of the illumination optical system of the comparative example, a large inward flare is observed in Fig. 9 . The inward flare of the illumination optical system corresponds to the outward coma aberration in the imaging optical system. Therefore, it is considered that the coma aberration is not sufficiently reduced when the comparative example is used as the illumination optical system.

[0044] Comparing Tables 3 and 7, the refractive power of surface S5 is almost the same. On the other hand, according to Table 2, the center thickness of the second lens of the example is 6.992 mm, and according to Table 5, the center thickness of the second lens of the comparative example is 2.500 mm.

[0045] According to Figure 6, when a parallel beam of light is incident at an angle of 23 degrees with the optical axis, the light beam is incident on the surface S5 of the example in an area above the optical axis. On the other hand, according to Figure 8, when a parallel beam of light is incident at an angle of 23 degrees with the optical axis, the light beam is incident on both the area above and below the optical axis on the surface S5 of the comparative example. In the comparative example, it is believed that the light beam incident on both the area above and below the optical axis on the surface S5 increases the coma aberration. Considering the shapes of the lenses of the example and the comparative example, it is believed that by adjusting the central thickness of the second lens, it is possible to adjust the area of ​​incidence of the light beam on the surface S5 when a parallel beam of light is incident at an angle of 23 degrees with the optical axis.

[0046] Therefore, the path of the light ray when a parallel light beam making an angle of 23 degrees with the optical axis is incident on the optical system in which the center thickness of the second lens is changed in the optical system of the example was determined. Note that the data other than the center thickness of the second lens of the optical system in which the center thickness of the second lens is changed is the same as that of Example 1.

[0047] FIG. 10 is a diagram showing the path of light rays when a parallel beam of light making an angle of 23 degrees with the optical axis is incident on an optical system in which the center thickness of the second lens is changed to 4.0 mm.

[0048] FIG. 11 is a diagram showing the path of light rays when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system in which the center thickness of the second lens is changed and the optical system is 5.5 mm.

[0049] FIG. 12 is a diagram showing the path of light rays when a parallel light beam making an angle of 23 degrees with the optical axis is incident on an optical system in which the center thickness of the second lens is changed and the optical system is 8.5 mm.

[0050] 10 to 12, when a parallel beam of light is incident at an angle of 23 degrees to the optical axis, the light beam is incident on surface S5 of each imaging optical system in a region above the optical axis. Therefore, it is believed that coma aberration can be reduced. The center thicknesses of the second lens, 4.0 mm, 5.5 mm, and 8.5 mm, normalized by the composite focal length of the imaging optical system in this example (34.697 mm), are 0.115, 0.159, and 0.245, respectively. On the other hand, an excessively large center thickness of the lens is undesirable because it increases the molding time during manufacturing and increases material costs. Therefore, it is preferable to set the center thickness of the second lens normalized by the composite focal length of the imaging optical system in the range of 0.1 to 0.25.

[0051] FIG. 13 is a diagram showing the curvature of field when the embodiment is considered as an imaging optical system. The horizontal axis of FIG. 13 indicates the coordinate of the image point position in the z-axis direction. The origin of the coordinates is point O, and the sign of the coordinate is negative on the side of the illumination target. The unit is millimeters. The vertical axis of FIG. 13 indicates the angle between the parallel light beam incident on surface S1 and the optical axis. The unit is degrees. 0.42T indicates the position of the image point on the tangential plane of a light beam with a wavelength of 0.42 micrometers, and 0.42S indicates the position of the image point on the sagittal plane of a light beam with a wavelength of 0.42 micrometers. 0.68T indicates the position of the image point on the tangential plane of a light beam with a wavelength of 0.68 micrometers, and 0.68S indicates the position of the image point on the sagittal plane of a light beam with a wavelength of 0.68 micrometers.

[0052] FIG. 14 shows distortion when the embodiment is considered as an imaging optical system. Distortion is the ratio of the lateral magnification of the imaging optical system to the lateral magnification of an ideal lens. The horizontal axis of FIG. 14 represents distortion, measured in percent. The vertical axis of FIG. 14 represents the angle between the parallel light beam incident on surface S1 and the optical axis, measured in degrees. Distortion at an angle of 20 degrees is approximately -5 percent. Because distortion is negative at relatively large angles, the illumination range of the illumination optical system is larger than that of an ideal optical system with zero distortion.

[0053] Generally, when the angle between the parallel light beam incident on the surface S1 and the optical axis is 20 degrees, the distortion is negative, and the absolute value of the distortion is preferably 5% or more.

[0054] FIG. 15 shows the axial chromatic aberration when the embodiment is considered as an imaging optical system. The horizontal axis in FIG. 15 represents the z-axis coordinate of the image point position. The origin of the coordinates is point O, and the sign of the coordinate is negative on the illumination target side. The unit is micrometers. The vertical axis in FIG. 15 represents the wavelength of the light ray. The unit is micrometers. The imaging optical system uses the d-line (588 nanometers) as its dominant wavelength. The horizontal axis coordinate of the d-line and the horizontal axis coordinate of the 488-nanometer wavelength light are the same, which reduces chromatic dispersion on the illumination surface of the illumination optical system. Generally, to reduce chromatic dispersion on the illumination surface of the illumination optical system, when the illumination optical system is considered as an imaging optical system for a light beam incident from the illumination target side, it is preferable to satisfy c / f<0.00292, where c is the focal range of the axial chromatic aberration of light rays with wavelengths from 0.420 micrometers to 0.680 micrometers, based on the d-line (588 nanometers).

Claims

1. An illumination optical system including a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, in that order from the illumination target side. When regarded as an imaging optical system for the light beam incident from the illumination target side to the illumination optical system, the combined focal length is f millimeters, the combined refractive power is Pt = 1 / f. Taking each surface of the three lenses as the first to sixth surfaces from the illumination target side, the refractive power of the fifth surface is P5, and the center thickness of the second lens is L2. An illumination optical system satisfying 1.3 < P5 / Pt 0.1 < L2 / f < 0.

25.

2. The illumination optical system according to claim 1, wherein when regarded as an imaging optical system for the light beam incident from the illumination target side to the illumination optical system, the ratio of the light rays reaching the image plane among the light rays incident at an angle of 25 degrees with respect to the optical axis on the illumination target side surface of the first lens is in the range of 14% to 20%.

3. The illumination optical system according to claim 1, wherein when regarded as an imaging optical system for the light beam incident from the illumination target side to the illumination optical system, with the F value being F, it satisfies F < 0.

7.

4. The illumination optical system according to claim 1, wherein when regarded as an imaging optical system for the light beam incident from the illumination target side to the illumination optical system, with the focus shift range of the axial chromatic aberration of the light rays with wavelengths from 0.420 micrometers to 0.680 micrometers based on the d line (588 nanometers) being c millimeters, it satisfies c / f < 0.00292.

5. The illumination optical system according to claim 1, wherein when regarded as an imaging optical system for the light beam incident from the illumination target side to the illumination optical system, the distortion of the light rays incident at an angle of 20 degrees with respect to the optical axis on the illumination target side surface of the first lens is negative, and its absolute value is 5% or more.

6. The illumination optical system according to claim 1, wherein the materials of the first lens, the second lens, and the third lens are acrylic, polycarbonate, and acrylic, respectively.

7. The illumination optical system according to claim 1, wherein the first lens is a biconvex lens, the second lens is a biconcave lens, and the third lens is a biconvex lens.

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