Optical reflection element

Abstract

This optical reflection element (100) comprises: a movable part (103) having a flat plate-shape that rotates about a rotation axis (R0); a reflection surface (M1a) that is disposed on an upper surface (103a) of the movable part (103); and at least one rib (131a, 131b) that is disposed on a lower surface (103b) of the movable part (103). The reflection surface (M1a) is irradiated with light (L1) that decreases in intensity with increasing distance from a central axis (C0). The rib (131a) in a specific region of the lower surface (103b) corresponding to the vicinity of the center of a region irradiated with the light (L1) in the reflection surface (M1a) has a substantially curved shape in plan view.

Description

Optical Reflective Elements

[0001] The present invention relates to an optical reflective element for scanning light.

[0002] Conventionally, optical reflecting elements that rotate a reflecting surface to scan light have been known. This type of optical reflecting element can be used, for example, in image display devices such as head-up displays. For example, a MEMS (Micro Electro Mechanical Systems) mirror is used as the optical reflecting element. Such optical reflecting elements are provided with a structure for suppressing deflection of the reflecting surface.

[0003] The following Patent Document 1 describes an optical scanning device in which intersecting linear ribs are formed on the underside of a plate-like movable part that rotates together with the reflective surface. With this configuration, the rigidity of the movable part is increased by the ribs, thereby suppressing deflection of the movable part and the reflective surface on the upper surface of the movable part.

[0004] Patent No. 7121258

[0005] However, through investigations by the inventors, it was found that in the above configuration, the ribs formed on the underside of the movable part cause diffraction of the light reflected by the reflective surface, which results in the light reflected by the reflective surface containing not only the original reflected light but also unwanted diffracted light that becomes noise in the optical scanning.

[0006] In view of the above problem, an object of the present invention is to provide an optical reflecting element that can suppress the influence of diffracted light due to the ribs while reinforcing a movable part having a reflecting surface with the ribs.

[0007] The optical reflecting element according to a first aspect of the present invention includes a flat movable portion that rotates about a rotation axis, a reflective surface disposed on an upper surface of the movable portion, and at least one rib disposed on a lower surface of the movable portion. The reflective surface is irradiated with light whose intensity decreases with increasing distance from a central axis. The rib in a specific region of the lower surface corresponding to the vicinity of the center of the light irradiation region on the reflective surface has a substantially curved shape in a plan view.

[0008] According to the optical reflecting element of this aspect, ribs are disposed on the lower surface of the movable part, thereby reinforcing the movable part with the ribs. This makes it possible to prevent bending of the movable part and the reflective surface disposed on its upper surface. Furthermore, ribs having a substantially curved shape are disposed in specific regions on the lower surface of the movable part. Therefore, diffracted light generated by changes in the shape of the reflective surface due to these ribs is dispersed, making it less likely that peaks will occur in the diffracted light. This effectively prevents diffracted light from the light near the center, where the intensity is high, from affecting the scanning of the light.

[0009] The optical reflecting element according to a second aspect of the present invention includes a flat movable portion that rotates about a rotation axis, a reflective surface disposed on an upper surface of the movable portion, and at least one rib disposed on a lower surface of the movable portion. The reflective surface is irradiated with light having a plurality of peak intensities near a central axis and whose intensity decreases with increasing distance from each of the peak intensities. The rib in a specific region of the lower surface corresponding to the vicinity of the center of the light-irradiated region on the reflective surface has a substantially curved shape in a plan view.

[0010] According to the optical reflecting element of this aspect, ribs are disposed on the lower surface of the movable part, thereby reinforcing the movable part with the ribs. This makes it possible to prevent bending of the movable part and the reflective surface disposed on its upper surface. Furthermore, ribs having a substantially curved shape are disposed in specific regions on the lower surface of the movable part. Therefore, diffracted light generated by changes in the shape of the reflective surface due to these ribs is dispersed, making it less likely that peaks will occur in the diffracted light. This effectively prevents diffracted light from the light near the center, where the intensity is high, from affecting the scanning of the light.

[0011] The optical reflecting element according to a third aspect of the present invention comprises a flat movable part that rotates about a rotation axis, a reflecting surface disposed on an upper surface of the movable part, a first rib disposed on a lower surface of the movable part and surrounding the center of the lower surface, and a second rib disposed on the lower surface outside the first rib and extending substantially parallel to the rotation axis, The first rib has a substantially curved shape in a plan view, and no other ribs are provided inside the first rib.

[0012] According to the optical reflecting element of this aspect, the first rib and the second rib are disposed on the underside of the movable part, thereby reinforcing the movable part with these ribs. This prevents the movable part and the reflective surface disposed on its upper surface from being warped. Furthermore, the second rib is disposed substantially parallel to the rotation axis, thereby preventing the second rib from increasing the moment of inertia of the movable part rotating about the rotation axis. This allows the movable part to rotate smoothly. Furthermore, substantially only the curved first rib is disposed in the area surrounding the center of the underside of the movable part. Therefore, the shape change of the reflective surface due to the first rib also substantially surrounds the center with a curve. Therefore, diffraction does not occur inside the shape change of the reflective surface, and the diffracted light generated by this shape change is dispersed, making it less likely to produce a peak. This effectively prevents the effect of diffraction by the first rib on light near the center, where the intensity of the irradiated light is high.

[0013] As described above, according to the present invention, it is possible to provide an optical reflecting element that can suppress the influence of diffracted light due to the ribs while reinforcing a movable portion having a reflecting surface with the ribs.

[0014] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0015] FIG. 1 is a plan view showing the configuration of an optical reflecting element according to an embodiment. FIG. 2 is a cross-sectional view showing the configuration of an optical reflecting element according to an embodiment. FIG. 3 is a diagram schematically showing the structure of a lower surface 103b of a movable portion according to an embodiment. FIG. 4 is a plan view showing the configuration of an optical deflector according to an embodiment. FIG. 5 is a diagram showing the configuration of an optical scanning device 20 according to an embodiment. FIG. 6 is a diagram schematically showing a light irradiation area on a reflecting surface and the light intensity distribution in the irradiation area according to an embodiment. FIG. 7(a) is a diagram schematically showing the configuration of a rib according to Comparative Example 1. FIG. 7(b) is a diagram showing a simulation result according to Comparative Example 1. FIG. 8(a) is a diagram schematically showing the configuration of a rib according to Example 1. FIG. 8(b) is a diagram showing a simulation result according to Example 1. FIG. 9(a) is a diagram schematically showing the configuration of a rib according to Comparative Example 2. FIG. 9(b) is a diagram showing a simulation result according to Comparative Example 2. FIG. 9(c) is a diagram schematically showing the configuration of a rib according to Comparative Example 3. FIG. 9(d) is a diagram showing a simulation result according to Comparative Example 3. FIG. 10( a) is a diagram schematically illustrating a rib configuration according to Example 2. FIG. 10( b) is a diagram illustrating simulation results according to Example 2. FIG. 10( c) is a diagram schematically illustrating a rib configuration according to Example 3. FIG. 10( d) is a diagram illustrating simulation results according to Example 3. FIG. 11 is a diagram schematically illustrating a rib arrangement method according to Modification Example 1. FIG. 12( a) is a diagram for explaining a simulation method according to Modification Example 1. FIG. 12( b) is a diagram for explaining a method for acquiring parameter values ​​indicating the intensity of diffracted light in a simulation according to Modification Example 1. FIG. 13 is a graph illustrating simulation results according to Modification Example 1. FIGS. 14( a) and 14(b) are diagrams for explaining other rib arrangement methods according to Modification Example 1. FIGS. 15( a) and 15(b) are diagrams schematically illustrating rib arrangement methods according to Modification Examples 2 and 3, respectively. FIG. 16 is a diagram schematically illustrating a light irradiation area on a reflecting surface and the light intensity distribution in the irradiation area according to Modification Example 2. 17(a) and 17(b) are diagrams schematically showing rib arrangement methods according to Modifications 4 and 5, respectively.FIGS. 18(a) and 18(b) are diagrams schematically illustrating rib arrangement methods according to Modifications 6 and 7, respectively. FIGS. 19(a) and 19(b) are diagrams schematically illustrating rib arrangement methods according to Modifications 8 and 9, respectively. FIG. 20(a) is a cross-sectional view showing an enlarged view of the configuration near the movable section according to the embodiment. FIG. 20(b) is a cross-sectional view showing an enlarged view of the configuration near the movable section according to Modification 10. FIG. 21 is a diagram schematically illustrating the light irradiation area on the reflecting surface and the light intensity distribution in the irradiation area according to Modification 11. FIGS. 22(a) to 22(c) are diagrams illustrating simulation results of beam spots generated on the detection surface by the configurations of Comparative Examples 1 to 3, respectively, according to Modification 11. FIGS. 23(a) to 23(c) are diagrams illustrating simulation results of beam spots generated on the detection surface by the configurations of Examples 1 to 3, respectively, according to Modification 11. FIG. 24 is a graph illustrating simulation results according to Modification 11. Fig. 25(a) is a diagram schematically showing a specific region and a method of arranging ribs according to Modification Example 1. Fig. 25(b) is a diagram schematically showing a region where curved ribs are arranged and a method of arranging the ribs according to a reference example.

[0016] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0018] For convenience, each figure is labeled with X, Y, and Z axes that are orthogonal to one another. The Z axis direction is the up-down direction of optical reflecting element 100, and the X axis direction and the Y axis direction are the long side direction and the short side direction, respectively, of optical reflecting element 100. The positive direction of the Z axis is the up direction of optical reflecting element 100.

[0019] FIG. 1 is a plan view showing the configuration of the optical reflecting element 100, and FIG. 2 is a cross-sectional view of the optical reflecting element 100 when the optical reflecting element 100 is cut along a plane parallel to the XZ plane at the position of the rotation axis R0 in FIG. 1.

[0020] 1, in this embodiment, the optical reflecting element 100 is configured by a meandering MEMS mirror. However, the optical reflecting element 100 is not limited to the meandering MEMS mirror, and may have other configurations as long as the movable part 103 can be rotated about the rotation axis R0.

[0021] The optical reflecting element 100 includes a support portion 101 , a pair of drive portions 102 , and a movable portion 103 .

[0022] 2, the support part 101, the pair of drive parts 102, and the movable part 103 share a common silicon substrate 121 made of silicon. The support part 101, the pair of drive parts 102, and the movable part 103 are connected by the silicon substrate 121. The support part 101 is configured by laminating a silicon substrate 122 made of silicon on the lower surface of the silicon substrate 121. A silicon oxide film is interposed between the silicon substrates 121 and 122. The rigidity of the support part 101 is increased by having two silicon substrates 121 and 122.

[0023] As shown in FIG. 1, the support portion 101 is a frame-shaped member having a rectangular outline in a plan view.

[0024] The driving unit 102 includes a substrate 110 and four piezoelectric actuators 111 formed on the upper surface of the substrate 110. The substrate 110 has a meandering shape that snakes in a direction perpendicular to the rotation axis R0. The thickness of the substrate 110 is constant. The substrate 110 is a part of the silicon substrate 121 described above.

[0025] The four piezoelectric actuators 111 are respectively disposed on the upper surface of four regions 110a of the substrate 110, which extend in a direction perpendicular to the rotation axis R0 (the Y-axis direction). Each piezoelectric actuator 111 is configured by sandwiching a piezoelectric body of a certain thickness between an upper electrode and a lower electrode.

[0026] The piezoelectric body is made of, for example, PZT (lead zirconate titanate). The upper electrode and the lower electrode are made of, for example, platinum. When a voltage (drive signal) is applied between the upper electrode and the lower electrode, the piezoelectric actuator 111 (piezoelectric body) expands and contracts. This causes the substrate 110 to bend, generating a drive force for driving the movable part 103.

[0027] The movable part 103 is supported by a pair of drive parts 102. The movable part 103 is a part of the silicon substrate 121 described above. In a plan view, the movable part 103 has a circular shape. However, the shape of the movable part 103 in a plan view may be another shape, such as a square.

[0028] The thickness of the movable part 103 is the same as the thickness of the silicon substrate 121 in Figure 2. The movable part 103 has a flat plate shape with an upper surface 103a and a lower surface 103b parallel to the XY plane. A mirror M1 is formed on the upper surface 103a of the movable part 103. In this example, the mirror M1 is formed over the entire upper surface 103a of the movable part 103.

[0029] The mirror M1 is formed by laminating an optical reflective film made of platinum, silver, or an alloy thereof on the upper surface 103a. The mirror M1 may be formed of an optical multilayer film made of these materials. Alternatively, the mirror M1 may be formed of a dielectric material. By forming the mirror M1, a reflective surface M1a is disposed on the upper surface 103a of the movable part 103. If the reflectivity of the upper surface 103a of the movable part 103 is high, the mirror M1 may be omitted and the upper surface 103a of the movable part 103 may be used as the reflective surface.

[0030] As will be described later, the reflecting surface M1a is irradiated with light whose intensity decreases with increasing distance from the central axis C0 (see FIGS. 5 and 6). That is, the intensity of this light has a Gaussian distribution. In this embodiment, the intensity of the light irradiated to the reflecting surface M1a has a similar Gaussian distribution over the entire circumference around the central axis C0. Such a light intensity distribution can be achieved, for example, by using a vertical cavity surface emitting laser (VCSEL) as the light source.

[0031] 2, ribs 131a and 131b are formed on the lower surface 103b of the movable part 103. The ribs 131a and 131b are made of silicon, similar to the silicon substrate 122. Each of the ribs 131a and 131b is arranged in an annular shape. Each of the ribs 131a and 131b has a wall shape with a substantially constant width and height.

[0032] FIG. 3 is a diagram schematically showing the structure of the lower surface 103 b of the movable portion 103 .

[0033] As shown in FIG. 3 , two ribs 131a and 131b, each having an annular shape in a plan view, are arranged on the lower surface 103b of the movable part 103. The ribs 131a and 131b are arranged concentrically with the center C1 of the lower surface 103b of the movable part 103. The rib 131a is included in a specific area CA1 set near the center of the lower surface 103b. The other ribs 131b are arranged along the outer periphery of the lower surface 103b. That is, the outer diameter D11 of the rib 131a is smaller than the diameter of the specific area CA1, and the outer diameter D12 of the other rib 131b is equal to the diameter of the movable part 103. The widths and heights of the ribs 131a and 131b are the same.

[0034] The specific area CA1 where the rib 131a is arranged is an area corresponding to the vicinity of the center of the light irradiation area on the reflecting surface M1a. In this embodiment, since the light irradiation area is circular, the specific area CA1 is also circular. The center of the specific area CA1 coincides with the center C1 of the lower surface 103b. The specific area CA1 may have the same size as an area where the intensity of light irradiated onto the reflecting surface M1a is equal to or greater than half the peak intensity. Alternatively, the specific area CA1 may be equal to or greater than the size of an area where the intensity of light irradiated onto the reflecting surface M1a is equal to or greater than half the peak intensity, and the specific area CA1 may be equal to or greater than the size of an area where the intensity of light irradiated onto the reflecting surface M1a is equal to or greater than half the peak intensity. ２ (e is Napier's constant) or less.

[0035] A structure in which silicon substrates 121 and 122 of a fixed thickness are stacked is used to manufacture optical reflecting element 100. The outline of this structure in a plan view is the same as the outline of optical reflecting element 100 in Fig. 1. Furthermore, a layer structure of piezoelectric actuator 111 is uniformly stacked on the upper surface of this structure.

[0036] The silicon substrate 122 on the lower surface side is removed by etching this structure. At this time, as shown in FIG. 2 , the silicon substrate 122 in the areas corresponding to the support portion 101 and the ribs 131 a, 131 b is left unremoved. As a result, the ribs 131 a, 131 b are formed on the lower surface 103 b of the movable portion 103. Furthermore, the thickness of the support portion 101 is ensured by the silicon substrate 122 left on the support portion 101.

[0037] Next, the layer structure of piezoelectric actuator 111 is removed by etching from the top surface of this layer structure, leaving only the region of piezoelectric actuator 111. Next, mirror M1 is vapor-deposited in the region of mirror M1. Furthermore, silicon substrates 121 and 122 are removed by etching in regions other than support portion 101, pair of drive portions 102, and movable portion 103. This completes the manufacture of optical reflecting element 100 having the shape shown in Figures 1 and 2.

[0038] In the configuration of Figure 1, when drive voltages of the same phase are applied to odd-numbered piezoelectric actuators 111 from the movable part 103 side, the piezoelectric bodies of these piezoelectric actuators 111 deform, and the odd-numbered substrates 110 (regions 110a) vibrate so as to bend. At this time, a drive voltage of the opposite phase to the drive voltage applied to the odd-numbered piezoelectric actuators 111 is applied to the even-numbered piezoelectric actuators 111 from the movable part 103 side. This deforms the piezoelectric bodies in the piezoelectric actuators 111, and the even-numbered substrates 110 (regions 110a) deform so as to bend. In this way, the deformation of each substrate 110 causes the movable part 103 to rotate about the rotation axis R0.

[0039] FIG. 4 is a plan view showing the configuration of the optical deflector 10. FIG. 5 is a diagram showing the configuration of the optical scanning device 20. FIG. 5 shows a cross-sectional view of the optical deflector 10 of FIG. 4 taken along a plane parallel to the YZ plane at position A-A. FIG. 5 also shows a cross-sectional view of the optical deflector 10 when the movable part 103 is in a neutral position (a position when in an inoperative state). In FIG. 5, the outer edge of the light L1 is indicated by a dashed line, and the central axis C0 of the light L1 (the optical axis of the optical system 300) is indicated by a dashed line.

[0040] As shown in Figures 3 and 4, optical reflecting element 100 is mounted in frame member 200. Frame member 200 has a rectangular shape that is long in the X-axis direction in plan view, and has a rectangular recess 201 into which optical reflecting element 100 fits. Frame member 200 has a constant thickness, and recess 201 has a constant depth. Recess 201 has a rectangular opening 202 formed therein that surrounds drive unit 102 and movable unit 103 of optical reflecting element 100 in plan view. Optical reflecting element 100 is mounted in recess 201 with an adhesive or the like.

[0041] 5, an optical system 300 for irradiating light L1 onto the reflecting surface M1a is disposed above the frame member 200. The optical system 300 includes a light source 301, a collimator lens 302, a polarizing beam splitter 303 (hereinafter referred to as "PBS 303"), and a quarter-wave plate 304.

[0042] The light source 301 is the above-mentioned vertical cavity surface emitting laser (VCSEL) and emits laser light (light L1) of a predetermined wavelength in the positive direction of the Y axis. The light source 301 is arranged so that the light is S-polarized with respect to the PBS 303. The light source 301 emits the light L1 at the same radiation angle all around. Therefore, the cross-sectional shape of the light L1 emitted from the light source 301 is circular.

[0043] The collimator lens 302 collimates the light L1 emitted from the light source 301 and makes it incident on the PBS 303. The PBS 303 has a cubic shape and has a polarization separation film 303a inside. The light L1 is incident on the polarization separation film 303a as S-polarized light, and is reflected by the polarization separation film 303a in the negative direction of the Z axis. The quarter-wave plate 304 converts the light L1 incident from the PBS 303 side into circularly polarized light. The light L1 transmitted through the quarter-wave plate 304 is incident on the reflecting surface M1a of the optical reflecting element 100.

[0044] Light L1 reflected by reflecting surface M1a in the positive direction of the Z axis passes through quarter-wave plate 304 again, where it is converted into P-polarized light with respect to polarization splitting film 303a. As a result, light L1 passes through polarization splitting film 303a and is emitted from PBS 303 in the positive direction of the Z axis. As a result, the movable part 103 and mirror M1 rotate about rotation axis R0 from the neutral position shown in FIG. 5 , the direction of light L1 emitted from PBS 303 rotates in the Y axis direction. As a result, light L1 scans a predetermined target area in the Y axis direction.

[0045] FIG. 6 is a diagram schematically showing an irradiation area E1 of the reflecting surface M1a with the light L1 and the intensity distribution of the light in the irradiation area E1.

[0046] Fig. 6 shows the illumination area E1 when the movable part 103 is in the neutral position. In the example of Fig. 6, the diameter D0 of the illumination area E1 of the light L1 is set to be slightly smaller than the diameter of the reflecting surface M1a. The central axis C0 of the light L1 (the center of the illumination area E1) coincides with the center of the reflecting surface M1a. As shown in Fig. 5, the central axis C0 of the light L1 when incident on the reflecting surface M1a is parallel to the Z axis.

[0047] The upper side of Fig. 6 shows the intensity distribution of light L1 in a direction parallel to the rotation axis R0 (X-axis direction), and the right side of Fig. 6 shows the intensity distribution of light L1 in a direction perpendicular to the rotation axis R0 (Y-axis direction). As shown in these figures, the intensity distribution of light L1 has a similar Gaussian distribution in both the direction parallel to the rotation axis R0 (X-axis direction) and the direction perpendicular to the rotation axis R0 (Y-axis direction). The intensity distribution of light L1 in other directions is also similar to the intensity distribution shown in Fig. 6. In other words, the intensity distribution of light L1 in the irradiation area E1 has a similar Gaussian distribution over the entire circumference.

[0048] As shown in FIG. 6, the intensity of the light L1 irradiating the reflecting surface M1a is 1 / e ２The above-mentioned region E1a is a circular region whose center is the center of the irradiation region E1 and the reflecting surface M1a. Furthermore, the region E1b, where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or greater than half the peak intensity P, is a circular region whose center is the center of the irradiation region E1 and the reflecting surface M1a. As described above, the specific region CA1 shown in Fig. 3 may have the same size as the region E1b shown in Fig. 6, or may have a size equal to or greater than the size of the region E1b and less than the size of the region E1a.

[0049] Incidentally, the movable part 103 may bend (dynamic bend) due to the inertial force generated during rotation. Furthermore, as described above, when the mirror M1 is formed on the upper surface 103a of the movable part 103, the difference in residual stress between the mirror M1 and the movable part 103 may cause bending (static bend) in the mirror M1 and the movable part 103. These bendings can be suppressed by forming ribs on the lower surface 103b of the movable part 103 to increase the strength (rigidity) of the movable part 103.

[0050] However, on the other hand, if ribs are formed on the lower surface 103b of the movable part 103, the formation of the ribs affects the flatness of the upper surface of the movable part 103, causing diffraction of the light L1 reflected by the reflecting surface M1a. As a result, the light L1 reflected by the reflecting surface M1a contains unnecessary diffracted light that becomes noise in the optical scanning, in addition to the original reflected light that is not diffracted.

[0051] The inventors have discovered a relationship between the configuration of the ribs formed on the lower surface 103b of the movable part 103 and the diffracted light generated in the light L1 reflected by the reflecting surface M1a. Based on this finding, by configuring the ribs 131a, 131b as described above, the movable part 103 can be reinforced and the influence of the diffracted light on the scanning of the light L1 can be effectively suppressed. Below, the above relationship discovered by the inventors will be described, along with a preferred configuration of the ribs formed on the lower surface 103b of the movable part 103.

[0052] FIG. 7A is a diagram schematically illustrating the configuration of a rib 132 according to a first comparative example.

[0053] In the comparative example, four ribs 132 that intersect with each other are arranged on the lower surface 103b of the movable part 103. The four ribs 132 extend linearly. Two ribs 132 extend parallel to the X axis, and the remaining two ribs 132 extend in the Y axis direction. The ribs 132 adjacent to each other in the X axis direction are arranged symmetrically with respect to the X axis on the lower surface 103b, and the ribs 132 adjacent to each other in the Y axis direction are arranged symmetrically with respect to the Y axis on the lower surface 103b. The distance between the ribs 132 adjacent to each other in the X axis direction is the same as the distance between the ribs 132 adjacent to each other in the Y axis direction.

[0054] The inventors conducted a simulation to determine the diffracted light that occurs in the light L1 reflected by the reflecting surface M1a when the rib 132 is configured as in the first comparative example.

[0055] In this simulation, it was assumed that a change in shape along the four ribs 132 occurred on the reflecting surface M1a. The irradiation area E1 of the light L1 was the entire reflecting surface M1a. The intensity distribution of the light L1 was set to a Gaussian distribution, as in FIG. 6. The reflecting surface M1a was set to a neutral position, as in FIG. 5. It was also assumed that the light L1 reflected by the reflecting surface M1a was focused on the detection surface using an ideal lens. The height and width of the change in shape on the reflecting surface M1a due to the ribs 132 (hereinafter referred to as the "derived ribs") were set to 100 nm and 50 μm, respectively. The diameter of the reflecting surface M1a was set to 1.4 mm, and the spacing between adjacent ribs 132 (the spacing between the derived ribs) was set to 0.4 mm.

[0056] FIG. 7B is a diagram showing the simulation results of Comparative Example 1 under the above conditions.

[0057] 7B shows the beam spots of the light L1 on the detection surface. As shown in FIG. 7B, in the configuration of the rib 132 according to the first comparative example, multiple beam spots B0, B1, and B2 were generated.

[0058] Beam spot B0 is a beam spot of light L1 (zeroth-order light) that is focused on the detection surface substantially without being subjected to diffraction by derivative ribs of the reflecting surface M1a based on the four ribs 132. Multiple beam spots B1 above and below beam spot B0 are beam spots of multiple orders of diffracted light generated when light L1 is diffracted by derivative ribs of the reflecting surface M1a based on the ribs 132 that extend parallel to the rotation axis R0. Multiple beam spots B2 on the left and right of beam spot B0 are beam spots of multiple orders of diffracted light generated when light L1 is diffracted by derivative ribs of the reflecting surface M1a based on the ribs 132 that extend perpendicular to the rotation axis R0.

[0059] In Comparative Example 1, these beam spots B0, B1, and B2 move in the Y-axis direction in response to the rotation of the movable part 103. Since the intensities of the beam spots B1 and B2 based on the diffracted light are relatively high, these beam spots B1 and B2 become noise in the scanning of the original beam spot B0.

[0060] FIG. 8A is a diagram schematically illustrating the configuration of the rib 132 according to the first embodiment.

[0061] In Example 1, only the inner rib 131a is arranged on the lower surface 103b of the movable part 103. In other words, the outer rib 131b is omitted from the configuration shown in Figure 3. The diameter of the rib 131a is set to 0.5 mm. The other simulation conditions are the same as those in Comparative Example 1.

[0062] FIG. 8B is a diagram showing the simulation results of Example 1 under the above conditions.

[0063] 7B, FIG. 8B shows the beam spot of light L1 on the detection surface. As shown in FIG. 8B, in the configuration of the rib 131a according to Example 1, only a beam spot B0 was generated. That is, in the derivative rib formed on the reflecting surface M1a based on the rib 131a according to Example 1, the distribution of beam spots based on diffracted light was hardly generated on the detection surface, and a beam spot B0 of the light L1 (zero-order light) that was condensed substantially without being subjected to the diffraction effect of the derivative rib was generated on the detection surface.

[0064] When the rib 131a has a curved shape as in Example 1, the derived rib generated on the reflecting surface M1a also has a curved shape. In this case, the diffracted light generated by the derived rib is dispersed according to the curved shape, so that the beam spots B1 and B2 based on the diffracted light do not substantially appear on the detection surface, as shown in Figure 8(b). In this way, the configuration of the rib 131a in Example 1 effectively suppresses the influence of the diffracted light based on the rib 131a.

[0065] The inventors further examined how diffracted light occurs for various rib configurations.

[0066] Figure 9(a) is a diagram showing a schematic diagram of the configuration of the rib 133 according to Comparative Example 2, and Figure 9(b) is a diagram showing the simulation results of the beam spot that occurs on the detection surface when the rib 133 according to Comparative Example 2 is arranged.

[0067] 9A, in Comparative Example 2, only one rib 133 extending linearly along one diameter of the movable part 103 is disposed on the lower surface 103b of the movable part 103. In this case, a derivative rib generated on the reflecting surface M1a by this rib 133 also extends linearly along the same diameter. The height and width of the rib 133 in the simulation are the same as those in Comparative Example 1. The other simulation conditions are also the same as those in Comparative Example 1.

[0068] 9B, in the configuration of Comparative Example 2, beam images B4 based on diffracted light were generated on the left and right of the beam spot B0. In this case as well, the intensity of the beam image B4 is relatively high, and therefore the beam image B4 becomes noise in the scanning of the original beam spot B0.

[0069] Figure 9(c) is a diagram showing a schematic diagram of the configuration of the rib 134 according to Comparative Example 3, and Figure 9(d) is a diagram showing the simulation results of the beam spot that appears on the detection surface when the rib 134 according to Comparative Example 3 is arranged.

[0070] As shown in FIG. 9C, in Comparative Example 3, four ribs 134 extending linearly along the four diameters of the movable part 103 are arranged on the lower surface 103b of the movable part 103. The four diameters are evenly arranged in the circumferential direction of the lower surface 103b. In this case, the derived ribs generated on the reflecting surface M1a by these ribs 133 also extend linearly along the same diameters. The height and width of the ribs 134 in the simulation are the same as those in Comparative Example 1. The other simulation conditions are also the same as those in Comparative Example 1.

[0071] 9D, in the configuration of Comparative Example 3, a beam image B5 based on diffracted light was generated radially from the beam spot B0. In this case as well, the intensity of the beam image B5 was relatively high, and therefore the beam image B5 became noise in the scanning of the original beam spot B0.

[0072] Figure 10(a) is a diagram showing a schematic diagram of the configuration of the rib 131a1 according to Example 2, and Figure 10(b) is a diagram showing the simulation results of the beam spot that occurs on the detection surface when the rib 131a1 of Example 2 is arranged.

[0073] 10A, in Example 2, the shape of the rib 131a1 is elliptical. The center of the ellipse coincides with the center of the lower surface 103b. The derivative rib generated on the reflecting surface M1a by the rib 131a1 also has a similar elliptical shape.

[0074] In the simulation of Example 2, the major diameter D21 of the rib 131a1 (derived rib) was set to be the same as the diameter of the rib 131a in Example 1. The minor diameter D22 of the rib 131a1 (derived rib) was set to 0.25 mm. Other simulation conditions were the same as those in Comparative Example 1.

[0075] 10B, in the configuration of Example 2, almost no image based on the diffracted light was generated around the beam spot B0, and essentially only the beam spot B0 was generated. According to the configuration of the rib 131a1 of Example 2, similar to Example 1, the influence of the diffracted light based on the rib 131a1 could be effectively suppressed.

[0076] Figure 10(c) is a diagram showing a schematic configuration of the rib 131a2 according to Example 3, and Figure 10(d) is a diagram showing the simulation results of the beam spot that occurs on the detection surface when the rib 131a2 according to Example 3 is arranged.

[0077] 10(c), in Example 3, the ribs 131a2 are arranged along a curved amplitude waveform. The center of the area surrounding the amplitude waveform coincides with the center of the lower surface 103. The derivative ribs generated on the reflecting surface M1a by the ribs 131a2 also have a shape that follows the same amplitude waveform.

[0078] In the simulation of Example 2, the width D31 of the rib 131a2 (derived rib) was set to 0.7 mm, and the amplitude D32 of the rib 131a2 (derived rib) was set to 0.25 mm. Other simulation conditions were the same as those of Comparative Example 1.

[0079] 10D, in the configuration of Example 3, almost no image based on the diffracted light was generated around the beam spot B0, and essentially only the beam spot B0 was generated. According to the configuration of the rib 131a2 of Example 3, similar to Example 1, the influence of the diffracted light based on the rib 131a2 could be effectively suppressed.

[0080] From the above simulation results, it can be said that it is preferable to arrange only ribs that are curved in plan view on the lower surface 103b of the movable part 103. This makes it possible to suppress the generation of high-intensity beam images due to diffracted light, and to suppress the influence of diffracted light on the scanning of light L1.

[0081] In particular, it is preferable to arrange only ribs having a curved shape in a plan view in a specific area CA1 on the lower surface 103b corresponding to the vicinity of the center of the reflecting surface M1a where the intensity of the irradiated light L1 is high, thereby suppressing the generation of high-intensity diffracted light and suppressing the influence of the diffracted light on the scanning of the light L1.

[0082] The area outside the specific area CA1 corresponds to the base of the Gaussian distribution shown in Figure 6, and therefore the intensity of the light L1 irradiated onto the reflecting surface M1a is low. Therefore, even if linear ribs are arranged in this outer area, the intensity of the diffracted light diffracted by the derivative ribs based on these ribs is significantly lower than the intensity of the original light L1 (zeroth-order diffracted light). Therefore, the influence of this diffracted light on the scanning of light L1 is significantly reduced.

[0083] From this perspective, linear ribs may be arranged in a plan view in the area outside the specific area CA1. This reinforces the outer area and further suppresses the deflection of the movable part 103 and the reflecting surface M1a. However, if it is desired to more thoroughly suppress the effect of diffracted light on the scanning of the light L1, it is preferable not to arrange linear ribs in the area outside the specific area CA1.

[0084] When the movable part 103 tilts from the neutral position, the irradiation area E1 deforms from a perfect circle in the tilting direction, and accordingly, the area near the center of the irradiation area E1, where the light intensity is high, also deforms from a perfect circle. However, due to this deformation, the portion that protrudes from the area (perfect circle) near the center at the neutral position is usually small compared to the entire area (perfect circle), and the intensity of the protruding portion is significantly lower than the peak intensity. Therefore, as described above, if the area of ​​the lower surface 103b corresponding to the area (perfect circle) near the center at the neutral position is set as the specific area CA1 and only curved ribs are arranged within this specific area CA1, even if the movable part 103 rotates and the reflecting surface M1a tilts from the neutral position during actual operation, the influence of diffracted light due to the ribs can be appropriately suppressed.

[0085] However, a specific area CA1 may be set on the lower surface 103b corresponding to the area obtained by combining the range in which the area near the center of the irradiation area E1 may deviate from a perfect circle during actual operation with the range of this perfect circle, and substantially only curved ribs may be arranged in this specific area CA1. This also applies to the cases in which the intensity distribution of the irradiation area E1 is not uniform, which will be described later in Modifications 2 and 3.

[0086] <Effects of the embodiment> According to the above embodiment, the following effects are achieved.

[0087] As shown in Figures 1 and 2, optical reflecting element 100 includes a flat movable portion 103 that rotates about a rotation axis R0, a reflecting surface M1a disposed on an upper surface 103a of movable portion 103, and at least one rib 131a, 131b disposed on a lower surface 103b of movable portion 103. As shown in Figure 6, light L1, whose intensity decreases with increasing distance from a central axis C0, is irradiated onto reflecting surface M1a. The central axis C0 of light L1 substantially coincides with the center of reflecting surface M1a. As shown in Figures 3, 8(a), 10(a), and 10(c), ribs 131a, 131a1, and 131a2 within a specific region CA1 on lower surface 103b corresponding to the vicinity of the center of irradiation region E1 of light L1 on reflecting surface M1a have a curved shape in a plan view.

[0088] According to this configuration, ribs 131a, 131b, 131a1, and 131a2 are disposed on the lower surface 103b of the movable portion 103, reinforcing the movable portion 103. This prevents deflection (dynamic deflection and static deflection) from occurring in the movable portion 103 and the reflecting surface M1a disposed on its upper surface 103a. Furthermore, curved ribs 131a, 131a1, and 131a2 are disposed in a specific area CA1 on the lower surface of the movable portion 103. Therefore, diffracted light generated by the shape change of the reflecting surface M1a due to these ribs (derived ribs) is dispersed, making it less likely for peaks to occur in the diffracted light, as shown in FIGS. 8(b), 10(b), and 10(d). This effectively prevents the diffracted light L1 near the center, which has a high intensity, from affecting the optical scanning.

[0089] As shown in FIGS. 3, 8A, and 10A, the ribs 131a and 131a1 in the specific area CA1 are arranged in an annular shape in a plan view.

[0090] According to this configuration, the ribs 131a and 131a1 can stably increase the strength of the center of the movable portion 103. Therefore, it is possible to effectively suppress bending of the center of the reflecting surface M1a, where the intensity of irradiated light is high.

[0091] As shown in FIG. 3 and FIG. 8A, the ribs 131a in the specific area CA1 are arranged along a perfect circle.

[0092] According to this configuration, when the intensity distribution (Gaussian distribution) of light L1 is uniform over the entire circumference, as shown in Figure 6, the intensity of the area of ​​the movable part 103 where the intensity of the irradiated light is high can be stably increased, and the deflection of the reflecting surface M1a in this area can be effectively suppressed.

[0093] As shown in FIG. 10A, the ribs 131a1 in the specific area CA1 are arranged along an ellipse.

[0094] According to this configuration, the rib 131a1 can stably increase the strength of the center of the movable portion 103. Therefore, it is possible to effectively suppress bending of the center of the reflecting surface M1a where the intensity of irradiated light is high.

[0095] As shown in FIG. 10C, the ribs 131a2 in the specific area CA1 are arranged along a curved amplitude waveform.

[0096] According to this configuration, curved ribs can be arranged in the area of ​​the movable part 103 where the intensity of irradiated light is high, thereby increasing the strength of the area of ​​the movable part where the intensity of irradiated light is high, and suppressing deflection of the reflective surface in this area.

[0097] As shown in FIG. 3, another rib 131b is disposed outside the specific area CA1.

[0098] According to this configuration, the other ribs 131b can increase the strength of the movable portion 103 on the outer side from the center, thereby widening the range in which deflection of the reflecting surface M1a can be suppressed.

[0099] As shown in FIG. 3, the other ribs 131b are arranged in an annular shape in a plan view.

[0100] According to this configuration, the other ribs 131b can increase the strength of the vicinity of the outer periphery of the movable portion 103. Therefore, deflection of the reflecting surface M1a in the vicinity of the outer periphery of the movable portion 103 can be suppressed.

[0101] As described with reference to FIG. 6, the specific area CA1 may have substantially the same size as the area E1b where the intensity of the light L1 irradiating the reflecting surface M1a is equal to or greater than half the peak intensity.

[0102] This makes it possible to suppress the influence of diffraction by the ribs 131a on at least the light L1 that is irradiated onto the reflecting surface M1a and that is included in the intensity range of at least half the peak intensity, thereby effectively suppressing the influence of diffracted light on the scanning of the light.

[0103] Alternatively, as described with reference to FIG. 6, the specific area CA1 is substantially equal to or larger than the area E1b where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or larger than half the peak intensity, and the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or larger than 1 / e of the peak intensity. ２ (e is Napier's constant) or less.

[0104] This makes it possible to suppress the influence of diffraction by the ribs on the light L1 included in the high intensity range, thereby more effectively suppressing the influence of diffracted light on the scanning light.

[0105] As shown in FIG. 2, a mirror M1 (optical reflection film) is formed on the upper surface 103a of the movable portion 103, thereby forming a reflection surface M1a.

[0106] This makes it possible to increase the reflectivity of the reflecting surface M1a and suppress surface roughness compared to when the upper surface 103a of the movable part 103 is used as a reflecting surface as is, thereby enabling scanning of the light L1 with high accuracy.

[0107] <Modification 1> Fig. 11 is a diagram schematically showing a method of arranging ribs according to Modification 1. Fig. 11 shows a plan view of the movable part 103 as viewed from the bottom side (Z-axis negative side).

[0108] As shown in Fig. 11 , in Modification Example 1, two ribs 131c are added compared to the embodiment in Fig. 3 . The two ribs 131c are arranged along the rotation axis R0 and connect the ribs 131a and 131b. The width and height of the ribs 131c are the same as those of the ribs 131a and 131b. The outer diameter of the inner rib 131a is approximately the same as the diameter of the specific area CA1.

[0109] 11, the two ribs 131c suppress deflection (especially static deflection) in the region of the movable part 103 between the ribs 131a and 131b. On the other hand, in this configuration, the derived rib corresponding to the rib 131c is included in the irradiation region E1 of the reflecting surface M1a with the light L1, and therefore, a peak of the diffracted light may occur due to this derived rib.

[0110] The inventors conducted a simulation to verify the relationship between the diameter of the rib 131a and the length of the rib 131c and the intensity of the diffracted light.

[0111] In this verification, as shown in FIG. 12(a), the outer rib 131b was omitted and the outer diameter D of the inner rib 131a was changed. As the outer diameter D increased, the length of the rib 131c was reduced. As in the simulation in the above embodiment, the light L1 was irradiated onto the entire reflecting surface M1a. The height and width of the ribs 131a and 131c were set in the same way as in the simulation in the above embodiment. The other simulations were the same as in the simulation in the above embodiment.

[0112] In this simulation, as shown in FIG. 12B, a reference line L0 was set on the detection surface, passing through the center of the beam spot and parallel to the diffraction direction, and the intensity of the diffracted light distributed along the reference line L0 was determined. More specifically, a value corresponding to the sum of the intensities of the diffracted light distributed along the reference line L0 in a range W1 outside the range W0 of the beam spot B0, which is not affected by diffraction, was obtained as a parameter value indicating the intensity of the diffracted light. This parameter value was obtained by integrating, over the range W1, the ratio of the intensity of the diffracted light at each position on the reference line L0 to the peak value of the intensity of the light L1 reflected by the reflecting surface M1a in the case where no ribs were provided on the lower surface 103b of the movable part 103. The range W1 was set to a range in which diffracted light substantially occurred.

[0113] FIG. 13 is a graph showing the simulation results.

[0114] In the graph of Fig. 13, the horizontal axis represents the diameter of the region between the two ribs 131c, which corresponds to the outer diameter D in Fig. 12. The vertical axis represents the parameter value indicating the intensity of the diffracted light described with reference to Fig. 12(b).

[0115] D1 indicated in the graph is the diameter of the region (corresponding to region E1b in FIG. 6) where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or greater than half of the peak intensity, and D2 is the diameter of the region (corresponding to region E1b in FIG. 6) where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or greater than 1 / e of the peak intensity. ２ D3 is the diameter of the above region (corresponding to region E1a in FIG. 6). D3 is half the diameter of the irradiation region E1 of the reflecting surface M1a with the light L1.

[0116] 13, the parameter value indicating the intensity of diffracted light decreased as the diameter (outer diameter D) of the region between the ribs 131c increased, and the decreasing trend of the parameter value became gentler after this diameter (outer diameter D) reached diameter D1 of region E1b. Furthermore, after this diameter (outer diameter D) reached diameter D2 of region E1a, the decreasing trend of the parameter value became even gentler, and after this diameter (outer diameter D) reached diameter D3b, the parameter value indicating the intensity of diffracted light remained near zero.

[0117] For this reason, it is preferable that the two linear ribs 131c are not disposed in a range of diameter smaller than the diameter D1 of the region (region E1b in FIG. 6) where the intensity of the light L1 irradiated to the reflecting surface M1a is half or more of the peak intensity, and the intensity of the light L1 irradiated to the reflecting surface M1a is 1 / e of the peak intensity. ２ It is more preferable that the above-mentioned region (region E1a in FIG. 6) is not disposed in a range of diameters smaller than diameter D2.

[0118] Therefore, it is preferable that the specific area CA1 where the curved rib is arranged has substantially the same size as the area (area E1b in FIG. 6) where the intensity of the light L1 irradiated to the reflecting surface M1a is half or more of the peak intensity. Alternatively, the specific area CA1 where the curved rib is arranged has substantially the same size as the area (area E1b in FIG. 6) where the intensity of the light L1 irradiated to the reflecting surface M1a is half or more of the peak intensity, and the intensity of the light L1 irradiated to the reflecting surface M1a is 1 / e of the peak intensity. ２It is preferable that the size of the area CA1 is equal to or smaller than the size of the above-mentioned area. This makes it possible to significantly reduce the influence of diffracted light caused by other ribs that extend linearly outside the area CA1. Therefore, it is possible to effectively suppress the influence of diffracted light on the scanning of the light L1.

[0119] <Effects of Modification Example 1> As shown in FIG. 11, the other ribs 131c extend in radial directions relative to the center of the lower surface 103b.

[0120] According to this configuration, the strength of the movable portion 103 can be increased up to the vicinity of the outer periphery by the other ribs 131c, and the range in which deflection of the reflecting surface M1a can be suppressed can be expanded up to the vicinity of the outer periphery.

[0121] As shown in FIG. 11, the direction in which the other rib 131c extends is parallel to the rotation axis R0.

[0122] This configuration can prevent the moment of inertia of the movable part 103 rotating about the rotation axis R0 from increasing due to the rib 131c, thereby allowing the movable part 103 to rotate smoothly.

[0123] As shown in FIG. 11, the other ribs 131c are arranged along a straight line.

[0124] This configuration allows the other ribs 131c to be formed smoothly, and also minimizes an increase in the moment of inertia caused by the other ribs 131c.

[0125] 11, the other ribs 131c are parallel to the rotation axis R0 in a plan view. However, as shown in FIGS. 14(a) and 14(b), the other ribs 131c may be slightly inclined (for example, by about 5°) with respect to the rotation axis R0 in a plan view. In other words, the other ribs 131c only need to be substantially parallel to the rotation axis R0 in a plan view. This also effectively prevents the moment of inertia of the movable part 103 rotating about the rotation axis R0 from increasing due to the ribs 131c.

[0126] 15(a) and 15(b) are diagrams schematically showing rib arrangement methods according to Modification Examples 2 and 3. Figures 15(a) and 15(b) show plan views of the movable part 103 as viewed from the bottom side (Z-axis negative side).

[0127] In the second and third modified examples, the irradiation area E1 when the movable part 103 is in the neutral position is changed to an ellipse. Therefore, the specific area CA1 is also elliptical, and the rib 131a arranged in the area CA1 is also elliptical. The other configurations are the same as those of the first modified example.

[0128] FIG. 16 is a diagram schematically showing an irradiation area E1 of the light L1 on the reflecting surface M1a and the intensity distribution of the light in the irradiation area E1 according to the second modification.

[0129] 16 shows the illumination area E1 when the movable part 103 is in the neutral position, as in FIG. 6. The minor axis of the ellipse defining the illumination area E1 is parallel to the rotation axis R0, and the major axis of the ellipse is perpendicular to the rotation axis R0. For example, the major axis is equal to the diameter of FIG. 6.

[0130] Such an illumination area E1 occurs, for example, when the light source 301 in Fig. 5 is an edge-emitting laser diode. The major axis of the ellipse corresponds to the fast axis of the laser diode, and the minor axis of the ellipse corresponds to the slow axis of the laser diode.

[0131] In this case, similarly to the first modification, it is preferable that the specific area CA1 where the curved rib is arranged has substantially the same size as the area E1b where the intensity of the light L1 irradiated to the reflecting surface M1a is equal to or greater than half of the peak intensity. Alternatively, the specific area CA1 where the curved rib is arranged has substantially the same size as the area E1b where the intensity of the light L1 irradiated to the reflecting surface M1a is equal to or greater than half of the peak intensity, and the intensity of the light L1 irradiated to the reflecting surface M1a is equal to or greater than 1 / e of the peak intensity. ２ It is preferable that the size of the area CA1 is equal to or smaller than the size of the above-mentioned area. This makes it possible to significantly reduce the influence of diffracted light caused by other ribs 131c that extend linearly outside the area CA1. Therefore, it is possible to effectively suppress the influence of diffracted light on the scanning of the light L1.

[0132] When the major axis of the irradiation area E1 is perpendicular to the rotation axis R0 as shown in Figure 16, the rib 131a arranged in the specific area CA1 can be set to, for example, an elliptical shape as shown in Figure 15(a). This allows the rib 131a to be smoothly arranged in the elliptical irradiation area E1. Furthermore, when the major axis of the irradiation area E1 is parallel to the rotation axis R0, the rib 131a arranged in the specific area CA1 can be set to, for example, an elliptical shape as shown in Figure 15(b). This allows the rib 131a to be smoothly arranged in the elliptical irradiation area E1.

[0133] In these cases, the specific area CA1 should be substantially the same size as the area E1b where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or greater than half of the peak intensity. Alternatively, the specific area CA1 where the curved rib is disposed should be substantially equal to or greater than the area E1b where the intensity of the light L1 irradiated onto the reflecting surface M1a is equal to or greater than half of the peak intensity, and the intensity of the light L1 irradiated onto the reflecting surface M1a should be 1 / e of the peak intensity. ２ It is preferable that the size of the area is equal to or smaller than the above-mentioned size.

[0134] As a result, even if another rib 131c extending linearly is disposed outside this area CA1, the influence of diffracted light generated by this other rib 131c can be significantly reduced, and the influence of diffracted light on the scanning of the light L1 can be effectively suppressed.

[0135] 16, when the irradiation area E1 is an ellipse, the specific area CA1 does not necessarily have to be an ellipse. For example, the specific area CA1 may be a circle whose diameter is the major axis of the area E1b, or may be a circle whose diameter is the major axis of the area E1a. Alternatively, the specific area CA1 may be a circle whose diameter is the minor axis of the area E1a, or may be a circle whose diameter is the length between the major axis of the area E1a and the major axis of the area E1b.

[0136] <Effects of Modification Example 2> As shown in FIGS. 15(a) and 15(b), the ribs 131a in the specific area CA1 are arranged along an ellipse.

[0137] 16, when the intensity distribution (Gaussian distribution) of light L1 is uneven in two orthogonal directions, the region near the center of the movable part where the intensity of irradiated light is high becomes elliptical. Therefore, by arranging ribs on the lower surface 103b along this ellipse, it is possible to stably increase the strength of the region of the movable part 103 where the intensity of irradiated light is high, while effectively suppressing the deflection of the reflecting surface M1a in this region.

[0138] <Modifications 4 to 7> Figures 17(a) and 17(b) are diagrams schematically showing rib arrangement methods according to Modifications 4 and 5, respectively. Figures 18(a) and 18(b) are diagrams schematically showing rib arrangement methods according to Modifications 6 and 7, respectively. Figures 17(a), (b) and 18(a), (b) show plan views of the movable part 103 as viewed from the bottom side (Z-axis negative side).

[0139] When linear ribs 131c are arranged outside specific area CA1 as in the above-described modification example 1, the shape of the curved ribs arranged in specific area CA1 is not limited to a circle or an ellipse, and may be, for example, a shape as shown in modification example 4 in Fig. 17(a) or a wave shape as shown in modifications 6 and 7 in Fig. 18(a) and 18(b). In these cases, too, by setting the diameter of specific area CA1 to be close to diameter D1 in Fig. 13 or in the range of diameters D1 to D2, the influence of diffracted light due to linear ribs 131c can be effectively suppressed, as in the verification results of Fig. 13.

[0140] Furthermore, the ribs arranged in the specific region CA1 do not necessarily have to be continuously connected, and for example, as shown in Fig. 17(b), they may be arranged along a circular shape with some discontinuities. Similarly, when the ribs arranged in the specific region CA1 have other shapes such as an ellipse or a wave shape, some of the ribs may be discontinuous. This also allows these ribs to increase the strength of the specific region CA1.

[0141] 19(a) and 19(b) are diagrams schematically showing rib arrangement methods according to Modifications 8 and 9, respectively. 19(a) and 19(b) show plan views of the movable part 103 as viewed from the bottom side (Z-axis negative side).

[0142] The other ribs 131c arranged outside the specific area CA1 do not necessarily have to be arranged along a straight line. For example, as shown in Modification 8 of Fig. 19(a), the other ribs 131c may be arranged along a curved amplitude waveform.

[0143] With this configuration, the diffracted light generated by the change in shape of the reflecting surface M1a due to the other ribs 131c is dispersed by the curved shape, making it less likely that a peak will occur in the diffracted light due to the other ribs 131c, thereby further suppressing the influence of the diffracted light due to the other ribs.

[0144] In this case, it is also preferable that the direction in which the other ribs 131c extend is substantially parallel to the rotation axis R0, as shown in Figure 19(a). This prevents the moment of inertia of the movable part 103 rotating about the rotation axis R0 from increasing compared to the other ribs 131c. This allows the movable part 103 to rotate smoothly.

[0145] Furthermore, the ribs arranged in the specific region CA1 only need to have a substantially curved shape, and the ribs arranged in the region CA1 may include a slight straight line portion. For example, as shown in Modification Example 9 of FIG. 19(b), the rib 131a arranged in the specific region CA1 may include a slight straight line portion P1. If the straight line portion included in the region CA1 is extremely small, the diffracted light resulting from this can be substantially ignored. Therefore, with this configuration, as with the above embodiment and each modification, the influence of diffracted light on the scanning of the light L1 can be effectively suppressed.

[0146] <Modification 10> In the above embodiment, as shown in FIG. 20(a) , the height of the ribs 131a, 131b is constant in the width direction of these ribs (in FIG. 20(a) , the Y-axis direction). However, the height of the ribs 131a, 131b is not limited to this, and may vary in the width direction of the ribs.

[0147] For example, as shown in Modification 10 of FIG. 20(b), the height of the ribs 131a and 131b may vary in the width direction of the ribs so that the lower surfaces of the ribs 131a and 131b are curved in the width direction of the ribs.

[0148] By varying the height of the ribs 131a and 131b in the width direction in this way, the shape (derived rib) formed on the reflecting surface M1a by the ribs 131a and 131b can be varied in the height direction, making it difficult for diffraction to occur due to this shape (derived rib).As a result, the effect of diffracted light by the ribs 131a and 131b on the scanning of the light L1 can be suppressed.

[0149] This configuration may be similarly applied to the ribs 131a1, 131a2, and other ribs 131c. Also, this configuration may be applied only to linear ribs that are likely to cause diffraction, or to ribs arranged in a specific area CA1 that corresponds to an area irradiated with high-intensity light.

[0150] In the above embodiment, as shown in Fig. 6, light whose intensity decreases with increasing distance from the central axis C0 is irradiated onto the reflecting surface M1a. That is, the intensity distribution of this light is a Gaussian distribution with only one peak near the central axis C0. In contrast, in Modification 11, light whose intensity has multiple peak intensities near the central axis C0 and whose intensity decreases with increasing distance from each peak intensity is irradiated onto the reflecting surface M1a.

[0151] FIG. 21 is a diagram schematically showing an irradiation area E1 of the reflecting surface M1a with the light L1 and the intensity distribution of the light in the irradiation area E1 according to the eleventh modification.

[0152] 6, Fig. 21 shows the illumination area E1 when the movable part 103 is in the neutral position. In the example of Fig. 21, the diameter D0 of the illumination area E1 of the light L1 is set to be slightly smaller than the diameter of the reflecting surface M1a. The central axis C0 of the light L1 (the center of the illumination area E1) coincides with the center of the reflecting surface M1a.

[0153] The upper side of Figure 21 shows the intensity distribution of light L1 in a direction parallel to the rotation axis R0 (X-axis direction), and the right side of Figure 21 shows the intensity distribution of light L1 in a direction perpendicular to the rotation axis R0 (Y-axis direction).

[0154] As shown in the intensity distribution on the right, the intensity distribution of light L1 has two peak intensities near the central axis C0. Here, the positions of these peak intensities are aligned in a direction perpendicular to the rotation axis R0 (Y-axis direction). As shown in the intensity distribution on the top, the intensity distribution of light L1 has a Gaussian distribution in a direction parallel to the rotation axis R0 (X-axis direction). The intensity of light L1 decreases with increasing distance from each peak intensity position. Light L1 with such an intensity distribution is emitted, for example, from a multimode laser light source.

[0155] In this case, the intensity of the light L1 irradiated onto the reflecting surface M1a is 1 / e of the peak intensity P. ２ The above-mentioned region E1a has a shape of two overlapping circles each centered on the positions of the two peak intensities, and the region E1b where the intensity of light L1 is equal to or greater than half the peak intensity P also has a shape of two overlapping circles each centered on the positions of the two peak intensities. The above-mentioned specific region CA1 may have substantially the same size as region E1b, or may have a size substantially equal to or greater than the size of region E1b but smaller than the size of region E1a. In a plan view, specific region CA1 may be a circular or elliptical region inscribed with region E1a or region E1b.

[0156] 22A to 22C are diagrams showing simulation results of beam spots generated on the detection surface by the configurations of comparative examples 1 to 3, respectively, in the eleventh modification.

[0157] 22(a) to 22(c) show schematic diagrams of the arrangements of ribs 132, 133, and 134 in Comparative Examples 1 to 3. The lower parts of Fig. 22(a) to 22(c) show simulation results of the beam spots that are generated on the detection surface when the configurations of Comparative Examples 1 to 3 are used.

[0158] The simulation conditions are the same as those of Comparative Examples 1 to 3 in Figures 7(a), (b) and Figures 9(a) to (d), except that the intensity distribution of light L1 irradiated onto the reflecting surface M1a is the intensity distribution shown in Figure 21.

[0159] As can be seen from the simulation results in the lower rows of Figures 22(a) to (c), with the rib arrangements of Comparative Examples 1 to 3, even when light L1 having the intensity distribution of Figure 21 is irradiated onto the reflecting surface M1a, in addition to the original beam spot B0, beam spots B1 and B2 and beam images B4 and B5 based on diffracted light are generated.

[0160] 23A to 23C are diagrams showing simulation results of beam spots generated on the detection surface by the configurations of Examples 1 to 3, respectively, according to Modification 11.

[0161] The upper parts of Figures 23(a) to (c) schematically show the arrangements of ribs 131a, 131a1, and 131a2 in Examples 1 to 3. The lower parts of Figures 23(a) to (c) show the simulation results of the beam spots that are generated on the detection surface when the configurations of Examples 1 to 3 are used.

[0162] The simulation conditions are the same as those of Examples 1 to 3 in Figures 8(a), (b) and Figures 10(a) to (d), except that the intensity distribution of light L1 irradiated onto the reflecting surface M1a is the intensity distribution of Figure 21.

[0163] As can be seen from the simulation results in the lower part of Figures 23(a) to (c), the rib arrangements of Examples 1 to 3 effectively suppress the generation of unwanted beam images based on diffracted light other than the original beam spot B0, even when light L1 having the intensity distribution of Figure 21 is irradiated onto the reflecting surface M1a.

[0164] FIG. 24 is a graph showing the results of a simulation under the same conditions as those in FIG. 13, in which the intensity of diffracted light generated when light L1 having the intensity distribution shown in FIG. 21 is irradiated onto the reflecting surface M1.

[0165] The simulation conditions are the same as those in Fig. 13, except that the intensity distribution of the irradiated light L1 is the intensity distribution shown in Fig. 21. The vertical and horizontal axes in Fig. 24 are also the same as those in Fig. 13.

[0166] Unlike the case of Fig. 13, in the simulation results of Fig. 24, in the range where the outer diameter D of the inner rib 131a in Fig. 12(a) reaches the diameter D1', the diffracted light intensity decreased as the outer diameter D increased, and in the range where the outer diameter D is from the diameter D1' to the diameter D2', the diffracted light intensity increased slightly as the outer diameter D increased. Then, when the outer diameter D became larger than the diameter D2', the diffracted light intensity decreased as the outer diameter D increased.

[0167] Here, the diameter D1' is 1 / e of the peak intensity P in the intensity distribution of FIG. ２ This corresponds to the width of the narrowed portion of region E1a, i.e., the width of region E1a in the X-axis direction at the position of rotation axis R0. Therefore, when the outer diameter D of inner rib 131a becomes equal to or larger than diameter D1', the two outer ribs 131c in Figure 12(a) no longer overlap region E1a, and the effects of diffraction by these ribs 131c are suppressed.

[0168] However, when the outer diameter D of the inner rib 131a is equal to or greater than the diameter D1', the inner rib 131a overlaps the peak of the intensity distribution of light L1, and the intensity of the diffracted light based on the inner rib 131a increases. Therefore, in the range where the outer diameter D of the inner rib 131a is between the diameter D1' and the diameter D2', the intensity of the diffracted light increases slightly as the outer diameter D increases. Then, when the outer diameter D of the inner rib 131a exceeds the diameter D2', the peak of the intensity distribution of light L1 is included inside the inner rib 131a. Therefore, in the range where the outer diameter D of the inner rib 131a exceeds the diameter D2', the intensity of the diffracted light decreases as the outer diameter D increases.

[0169] Therefore, as in Modification Example 11, when the intensity distribution of light L1 has multiple peaks, it is preferable to set the area where the inner rib 131a is arranged, i.e., the area of ​​the specific area CA1, to a size that includes all of the peaks. In this case, the specific area CA1 may be circular or elliptical. For example, when the peaks are aligned in one direction as shown in FIG. 21, the specific area CA1 may be elliptical in shape with its major axis aligned in the direction in which the peaks are aligned. Alternatively, the specific area CA1 may have a shape similar or nearly similar to that of the area E1a. By setting the specific area CA1 in this manner, the influence of diffracted light can be effectively suppressed.

[0170] In the above-described modified example 1, light L1, whose intensity decreases with increasing distance from the central axis, is irradiated onto the reflecting surface M1a, and a specific area CA1 is set as shown in Fig. 25(a). The center C1 of the lower surface 103b and the center C2 of the irradiation area E1 are substantially coincident with each other in a plan view.

[0171] In contrast, in the reference example, as shown in Fig. 25(b), light with a uniform intensity distribution is irradiated onto the reflecting surface M1a. In this case, the area of ​​the region CB1 where the curved rib 131a is arranged is preferably set to be larger than the area of ​​the lower surface 103b outside the region CB1. Alternatively, when the movable part 103 is in the neutral position, the area of ​​the region CB1 is preferably set to be larger than the area of ​​the region corresponding to the irradiation region E1 outside the region CB1.

[0172] This increases the proportion of the amount of light included in the area of ​​the reflecting surface M1a corresponding to the area CB1 out of the total amount of light irradiated onto the reflecting surface M1a, thereby increasing the proportion of light that does not undergo diffraction, thereby suppressing the effect of diffracted light on the scanning light.

[0173] 25(b), even if the center C1 of the lower surface 103b and the center C2 of the irradiation area E1 are misaligned in plan view, the ratio of the amount of non-diffracted light to the total amount of light irradiated onto the reflecting surface M1a remains the same as when the centers C1 and C2 are aligned. Therefore, by setting the area CB1 as described above, the effect of diffracted light on the scanning light can be similarly suppressed even when the centers C1 and C2 are misaligned.

[0174] <Other Modifications> In the above embodiment, the optical system 300 in Fig. 5 is illustrated as an example of an optical system that irradiates the reflecting surface M1a with light, but the configuration of the optical system is not limited to this. For example, the PBS 303 and the quarter-wave plate 304 may be omitted from the optical system 300 in Fig. 5. In this case, when the movable part 103 is in the neutral position, the light L1 is irradiated obliquely onto the reflecting surface M1a so that the central axis C0 is inclined by a predetermined angle with respect to the normal to the reflecting surface M1a.

[0175] When the optical system is configured in this way, the irradiated area E1 of the reflecting surface M1a is not a perfect circle but a curved ring shape that is long in the direction in which the central axis C0 is tilted. In this case, as in the above, it is preferable that the area CA1 near the center has substantially the same size as the area in this irradiated area E1 where the light intensity is equal to or greater than half the peak intensity, or the area CA1 is substantially equal to or greater than the size of the area where the light intensity irradiated to the reflecting surface is equal to or greater than half the peak intensity, and the light intensity irradiated to the reflecting surface is 1 / e of the peak intensity. ２ It is preferable that the size of the region is equal to or smaller than (e is Napier's constant).

[0176] Furthermore, in the above-described first to ninth modified examples, the direction in which the other ribs 131c extend is substantially parallel to the rotation axis R0, but the direction in which the other ribs 131c extend may be non-parallel to the rotation axis R0.

[0177] Furthermore, in the above embodiment and modified example, the central axis C0 of the light L1 substantially coincides with the center of the reflecting surface M1a (the center of the upper surface 103a of the movable part 103), but the central axis C0 of the light L1 may be deviated from the center of the reflecting surface M1a (the center of the upper surface 103a of the movable part 103). For example, even if the central axis C0 of the light L1 is slightly deviated from the center of the reflecting surface M1a (the center of the upper surface 103a of the movable part 103) in a direction parallel to the rotation axis R0, the scanning of the light L1 itself can be performed in the same way.

[0178] Furthermore, in the above-described embodiment and modified examples, the height and width of the ribs arranged within the specific area CA1 are the same as the height and width of the ribs arranged outside this area CA1, but one or both of the heights and widths of these ribs may be different from each other.

[0179] Furthermore, in the above embodiment, a laser light source is used as the light source 301, but this is not limiting, and for example, a light emitting diode may be used as the light source 301.

[0180] Furthermore, the device to which the optical reflecting element 100 and the optical deflector 10 are applied is not particularly limited, and may be any of various devices that require a configuration in which light is scanned by rotating the reflecting surface M1a.

[0181] The embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical idea defined in the claims.

[0182] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0183] (Technology 1) An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflective surface arranged on an upper surface of the movable part; and at least one rib arranged on a lower surface of the movable part, wherein light whose intensity decreases with increasing distance from a central axis is irradiated onto the reflective surface, and the rib within a specific area on the lower surface corresponding to the vicinity of the center of the light irradiated area on the reflective surface has a substantially curved shape in a planar view.

[0184] According to this technology, ribs are placed on the underside of the movable part, reinforcing the movable part with the ribs. This makes it possible to prevent bending of the movable part and the reflective surface placed on its upper surface. Furthermore, ribs with a substantially curved shape are placed in specific areas on the underside of the movable part. This disperses diffracted light caused by changes in the shape of the reflective surface due to these ribs, making it less likely that peaks will occur in the diffracted light. This effectively reduces the effect of diffraction by the ribs on light near the center where the intensity of the irradiated light is high.

[0185] (Technology 2) The optical reflecting element according to Technology 1, wherein the ribs in the specific region are arranged in a ring shape in a plan view.

[0186] According to this technology, the strength of the vicinity of the center of the movable part can be stably increased by the rib, and therefore, deflection of the vicinity of the center of the reflecting surface where the intensity of the irradiated light is high can be effectively suppressed.

[0187] (Technology 3) The optical reflecting element according to Technology 2, wherein the ribs in the specific region are arranged along a perfect circle.

[0188] According to this technology, when the light intensity distribution (Gaussian distribution) is uniform around the entire circumference, it is possible to stably increase the intensity of the area of ​​the movable part where the intensity of the irradiated light is high, and to effectively suppress the deflection of the reflective surface in this area.

[0189] (Technology 4) The optical reflecting element according to Technology 2, wherein the ribs in the specific region are arranged along an ellipse.

[0190] According to this technology, when the light intensity distribution (Gaussian distribution) is uneven in two orthogonal directions, the specific region of the movable part where the irradiated light intensity is high will have an elliptical shape. Therefore, by arranging ribs on the underside along this ellipse, it is possible to stably increase the strength of the region of the movable part where the irradiated light intensity is high, while effectively suppressing the deflection of the reflective surface in this region.

[0191] (Technology 5) The optical reflecting element according to any one of Technologies 1 to 4, wherein the ribs in the specific region are arranged along a curved amplitude waveform.

[0192] This technology allows curved ribs to be placed in areas of the movable part where the intensity of irradiated light is high, thereby increasing the strength of the areas of the movable part where the intensity of irradiated light is high and suppressing deflection of the reflective surface in these areas.

[0193] (Technology 6) The optical reflecting element according to any one of Technologies 1 to 5, characterized in that other ribs are arranged outside the specific region.

[0194] According to this technology, the strength of the movable portion on the outer side can be increased by using other ribs, thereby widening the range in which deflection of the reflecting surface can be suppressed.

[0195] (Technology 7) The optical reflecting element according to Technology 6, wherein the other ribs extend in radial directions relative to the center of the lower surface.

[0196] According to this technique, the strength of the movable portion can be increased up to the vicinity of the outer periphery by the other ribs, and the range in which deflection of the reflecting surface can be suppressed can be expanded up to the vicinity of the outer periphery.

[0197] (Technology 8) The optical reflecting element according to Technology 7, wherein the direction in which the other ribs extend is substantially parallel to the rotation axis.

[0198] This technique can prevent the moment of inertia of the movable part rotating about the rotation axis from being increased by other ribs, thereby allowing the movable part to rotate smoothly.

[0199] (Technology 9) The optical reflecting element according to Technology 7 or 8, characterized in that the other ribs are arranged along straight lines.

[0200] This technique allows the other ribs to be formed smoothly, and if the other ribs are parallel to the rotation axis, the increase in the moment of inertia caused by the other ribs can be minimized.

[0201] (Technology 10) The optical reflecting element according to Technology 7 or 8, characterized in that the other ribs are arranged along a curved amplitude waveform.

[0202] According to this technique, diffracted light caused by changes in the shape of the reflecting surface due to other ribs is dispersed, making it difficult for peaks to appear in the diffracted light due to other ribs, thereby suppressing the influence of diffracted light due to other ribs.

[0203] (Technology 11) The optical reflecting element according to Technology 6, wherein the other ribs are arranged in an annular shape in a plan view.

[0204] According to this technique, the strength of the area around the outer periphery of the movable part can be increased by the additional ribs, thereby suppressing deflection of the reflecting surface around the outer periphery of the movable part.

[0205] (Technology 12) In the optical reflecting element described in any one of Technologies 1 to 11, the specific region has substantially the same size as a region where the intensity of the light irradiated onto the reflecting surface is equal to or greater than half of the peak intensity.

[0206] This technique can suppress the influence of diffraction by the ribs on at least light that is irradiated onto the reflecting surface and that falls within an intensity range equal to or greater than half the peak intensity, thereby effectively suppressing the influence of diffracted light on the scanning light.

[0207] (Technology 13) In the optical reflecting element according to any one of technologies 1 to 11, the specific region is substantially equal to or larger than the size of a region where the intensity of the light irradiated on the reflecting surface is equal to or larger than half of the peak intensity, and the intensity of the light irradiated on the reflecting surface is 1 / e of the peak intensity. ２ (e is Napier's constant) or more.

[0208] This technique can suppress the influence of diffraction by the ribs on light that falls within a high-intensity range among light irradiated onto the reflective surface, thereby more effectively suppressing the influence of diffracted light on the scanning light.

[0209] (Technology 14) The optical reflecting element according to any one of Technologies 1 to 13, characterized in that the height of the rib changes continuously in the width direction of the rib.

[0210] This technology allows the height of the ribs to vary in the width direction, which in turn allows the shape of the reflective surface created by the ribs to vary in the height direction, making diffraction less likely to occur, thereby reducing the effect of diffracted light on the scanning light.

[0211] (Technology 15) The optical reflecting element according to any one of Techniques 1 to 14, wherein the reflecting surface is arranged by forming an optical reflecting film on an upper surface of the movable part.

[0212] This technique can increase the reflectivity of the reflective surface and suppress surface roughness compared to when the upper surface of the movable part is used as the reflective surface, thereby enabling high-precision scanning of light.

[0213] (Technology 16) An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflecting surface arranged on an upper surface of the movable part; and at least one rib arranged on a lower surface of the movable part; wherein light having a plurality of peak intensities near a central axis and decreasing in intensity with increasing distance from the position of each of the peak intensities is irradiated onto the reflecting surface; and wherein the rib within a specific region of the lower surface corresponding to the vicinity of the center of the light irradiated area on the reflecting surface has a substantially curved shape in a planar view.

[0214] According to this technology, ribs are placed on the underside of the movable part, reinforcing the movable part with the ribs. This makes it possible to prevent bending of the movable part and the reflective surface placed on its upper surface. Furthermore, ribs with a substantially curved shape are placed in specific areas on the underside of the movable part. This disperses diffracted light caused by changes in the shape of the reflective surface due to these ribs, making it less likely that peaks will occur in the diffracted light. This effectively reduces the effect of diffraction by the ribs on light near the center where the intensity of the irradiated light is high.

[0215] (Technology 17) An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflecting surface arranged on the upper surface of the movable part; a first rib arranged on the lower surface of the movable part and surrounding the center of the lower surface; and a second rib arranged on the lower surface outside the first rib and extending substantially parallel to the rotation axis, wherein the first rib has a substantially curved shape in a planar view; and no other ribs are provided inside the first rib.

[0216] According to this technology, first and second ribs are disposed on the underside of the movable part, reinforcing the movable part with these ribs. This prevents deflection of the movable part and the reflective surface disposed on its upper surface. Furthermore, because the second rib is disposed substantially parallel to the rotation axis, the second rib prevents the moment of inertia of the movable part rotating about the rotation axis from increasing. This allows the movable part to rotate smoothly. Furthermore, substantially only the curved first rib is disposed in the area surrounding the center of the underside of the movable part. Therefore, the shape change of the reflective surface due to the first rib also substantially surrounds the center with a curve. Therefore, diffraction does not occur inside the shape change of the reflective surface, and the diffracted light generated by this shape change is dispersed, making it less likely to produce a peak. This effectively prevents the effect of diffraction by the first rib on light near the center, where the intensity of the irradiated light is high.

[0217] 100 Optical reflecting element 103 Movable part 103a Upper surface 103b Lower surface 131a, 131b, 131c, 131a1, 131a2 Rib CA1 Specific area E1 Irradiation area E1a Area (1 / e of peak intensity) ２E1b region (region of intensity equal to or greater than half the peak intensity) L1 light M1a reflecting surface

Claims

1. An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflective surface arranged on an upper surface of said movable part; and at least one rib arranged on a lower surface of said movable part, wherein light whose intensity decreases with increasing distance from a central axis is irradiated onto said reflective surface, and wherein said rib within a specific area of ​​said lower surface corresponding to the vicinity of the center of the area irradiated by said light on said reflective surface has a substantially curved shape in a planar view.

2. An optical reflecting element as described in claim 1, characterized in that the ribs in the specific region are arranged in a ring shape when viewed in a plane.

3. An optical reflecting element as described in claim 2, characterized in that the ribs in the specific region are arranged along a perfect circle.

4. An optical reflecting element according to claim 2, characterized in that the ribs in the specific region are arranged along an ellipse.

5. An optical reflecting element according to claim 1, characterized in that the ribs in the specific region are arranged along a curved amplitude waveform.

6. An optical reflecting element according to claim 1, characterized in that other ribs are arranged outside the specific area.

7. An optical reflecting element according to claim 6, characterized in that the other ribs extend in a radial direction relative to the center of the lower surface.

8. An optical reflecting element according to claim 7, characterized in that the direction in which the other ribs extend is substantially parallel to the rotation axis.

9. The optical reflecting element according to claim 7, wherein the other ribs are arranged along a straight line.

10. An optical reflecting element according to claim 7, characterized in that the other ribs are arranged along a curved amplitude waveform.

11. An optical reflecting element according to claim 6, characterized in that the other ribs are arranged in an annular shape in a plan view.

12. An optical reflecting element as described in claim 1, characterized in that the specific region has a size substantially the same as that of an area where the intensity of the light irradiated onto the reflecting surface is equal to or greater than half the peak intensity.

13. In the optical reflecting element according to claim 1, the specific region is substantially equal to or larger than the size of an area where the intensity of the light irradiated to the reflecting surface is equal to or larger than half the peak intensity, and the intensity of the light irradiated to the reflecting surface is equal to or smaller than 1 / e of the peak intensity. ２ (e is Napier's constant) or more.

14. An optical reflecting element according to claim 1, wherein the height of said rib varies continuously in the width direction of said rib.

15. An optical reflecting element according to claim 1, characterized in that the reflecting surface is arranged by forming an optical reflecting film on the upper surface of the movable portion.

16. An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflective surface arranged on an upper surface of the movable part; and at least one rib arranged on a lower surface of the movable part, wherein light having a plurality of peak intensities near a central axis and decreasing in intensity with increasing distance from the position of each of the peak intensities is irradiated onto the reflective surface, and the rib within a specific area of ​​the lower surface corresponding to the vicinity of the center of the light irradiated area on the reflective surface has a substantially curved shape in a planar view.

17. An optical reflecting element comprising: a flat movable part that rotates about a rotation axis; a reflective surface arranged on an upper surface of the movable part; a first rib arranged on a lower surface of the movable part surrounding the center of the lower surface; and a second rib arranged on the lower surface outside the first rib and extending substantially parallel to the rotation axis, wherein the first rib has a substantially curved shape in a planar view; and no other ribs are provided inside the first rib.

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