Light deflector

Abstract

To provide a light deflector in which a dynamic surface deformation of the reflection surface of a mirror part is improved.SOLUTION: A mirror part 11 has a body part 22 and a rib structure 24 on a back surface side. In an elliptic rib 26 of the rib structure 24, the outer circumference extends along the circumference of an outside ellipse of which longer axis and shorter axis overlap with a vertical rotary shaft Wy and a lateral rotary shaft Wx, respectively, and the inner circumference extends along the circumference of an inner ellipse of which longer axis and shorter axis overlap with a vertical rotary shaft Wy and a lateral rotary shaft Wx, respectively.SELECTED DRAWING: Figure 2B

Description

[Technical field]

[0001] The present invention relates to an optical deflector based on a Micro Electro Mechanical System (MEMS). [Background technology]

[0002] Patent Document 1 discloses a MEMS optical deflector in which a rib structure is added to the back side of the mirror body to strengthen the rigidity of the mirror. According to this optical deflector, the rib structure has a circular or elliptical equal-width annular rib and a spreading rib that protrudes from the equal-width annular rib toward each torsion bar while spreading. The spreading rib is connected at its tip to the tip of a lateral extension protruding from the torsion bar in the width direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-170376 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical deflector of Patent Document 1, the equal-width annular rib increases the rigidity of the mirror portion, but there is still room for improvement in suppressing dynamic deformation of the mirror surface.

[0005] An object of the present invention is to provide an optical deflector which has an improved effect of suppressing dynamic surface deformation of the mirror surface. [Means for solving the problem]

[0006] The optical deflector of the present invention comprises: A support member; a mirror portion having a circular main body with a reflective surface and a rib structure formed on a rear surface of the main body; a pair of torsion bars extending along the rotation axis on both sides of the mirror section in the direction of the rotation axis and connected to the support member and the mirror section at both ends; an actuator coupled to a side edge of each torsion bar for rotating each torsion bar back and forth about the rotation axis; An optical deflector comprising: The rotation axis is defined as a vertical axis, and an axis perpendicular to the vertical axis at the center of the mirror portion is defined as a horizontal axis, an outer ellipse having a major axis and a minor axis respectively lying on the vertical axis and the horizontal axis when viewed from behind the mirror portion, and an inner ellipse located inside the outer ellipse and having a major axis and a minor axis respectively lying on the horizontal axis and the vertical axis, defining a specified azimuth angle range within a range of ±α on each side of the horizontal axis direction relative to the center, with the azimuth angle on each side being 0° on the horizontal axis; The rib structure includes an elliptical rib formed on the inside of the periphery of the outer ellipse, including on the periphery of the outer ellipse; The elliptical rib has an outer periphery formed on the circumference of the outer ellipse at least in each specified azimuth angle range, and an inner periphery formed on the circumference of the inner ellipse. Effect of the Invention

[0007] According to the present invention, the elliptical rib projects sufficiently toward the periphery of the main body of the mirror, while forming a narrow inner elliptical recess in the vertical axis direction on the inner peripheral side. This balances the rigidity of each part of the circular reflective surface of the mirror during reciprocal rotation around the rotation axis, and as a result, dynamic deformation of the reflective surface can be sufficiently suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram of the optical deflector as viewed obliquely from the front. [Figure 2A] 2 is a perspective view of an inner structural portion of the optical deflector as viewed obliquely from the front side. FIG. [Figure 2B] 2 is a perspective view of an inner structural portion of the optical deflector as viewed obliquely from the rear side. FIG. [Figure 3A]FIG. [Figure 3B] 4 is a diagram showing, by symbols, the dimensions of each part of the mirror part as viewed from the rear side. FIG. [Figure 3C] 3B is a cross-sectional view taken along the line F3C-F3C in FIG. 3A. [Figure 4A] FIG. 4 is a front view of the inner bar portion of the torsion bar. [Figure 4B] FIG. 4 is a front view of the outer bar portion of the torsion bar. [Diagram 5] FIG. 11 is a perspective view of a mirror portion of a comparative example when viewed obliquely from the rear side. [Figure 6A] 4 is a heat map of the amount of displacement in the thickness direction of each part of the main body when the mirror portion of the optical deflector of the first embodiment is rotated back and forth under specified conditions. FIG. [Figure 6B] 4 is a diagram showing the amount of displacement in the thickness direction of the mirror portion at a vertical axis position of 0 μm when the mirror portion of the optical deflector according to the first embodiment is rotated back and forth under predetermined conditions. FIG. [Figure 6C] 4 is a diagram showing the amount of displacement in the thickness direction of the mirror portion at a horizontal axis position of 150 μm when the mirror portion of the optical deflector according to the first embodiment is rotated back and forth under specified conditions. FIG. [Figure 6D] 4 is a heat map diagram of RMS (wavefront aberration) when the mirror portion of the optical deflector according to the first embodiment is rotated back and forth under predetermined conditions. FIG. [Figure 7A] FIG. 6B is a comparative diagram to FIG. 6A. [Figure 7B] FIG. 6B is a comparative diagram. [Figure 7C] FIG. 6C is a comparative diagram. [Figure 7D] A comparative diagram to FIG. 6D. [Figure 8] This figure shows that when the width of the inner bar portion is made wider at the end on the inner actuator side than at the end on the mirror portion side, stress concentration caused by twisting of the inner bar portion can be shifted toward the mirror portion side. [Figure 9A] 13 is a perspective view of an inner structural portion provided in an optical deflector according to a second embodiment, as viewed from the front side. FIG. [Figure 9B]13 is a perspective view of an inner structural portion provided in an optical deflector according to a second embodiment, as viewed from the rear side. FIG. [Figure 10A] FIG. 9C is an enlarged rear view of the area including the mirror portion in FIG. 9B. [Figure 10B] FIG. 10B is a rear view showing positions etc. of FIG. 10A. [Figure 10C] FIG. 10B is a diagram showing the specified azimuth angle range in the rear view of FIG. 10A. [Figure 10D] FIG. 10B is an enlarged rear view in which the rib structure in FIG. 10A is replaced with another rib structure. [Figure 11A] 10C is a cross-sectional view taken along line F11A-F11A in FIG. 10B. [Figure 11B] 10B is a cross-sectional view taken along the line F11B-F11B in FIG. 10B. [Figure 12] FIG. 11 is a diagram showing three comparative examples of a mirror portion. [Figure 13A] FIG. 13 is a table showing dynamic surface deformation for the comparative example of FIG. 12. [Figure 13B] 13 is a graph showing dynamic surface deformation for the comparative example of FIG. 12. [Figure 14] 13A-13C are grayscale images of heat maps of the dynamic deformation of the reflective surface of the body for each rib structure. [Figure 15] 15 is a graph comparing dynamic surface deformation for the rib structure of FIG. 14. [Figure 16] 15 is a graph comparing mechanical run-out angles for the rib structures of FIG. 14. [Figure 17] 1 is a heat map of stress distribution in an investigation of the cause of low mechanical run-out angle in a rib structure. [Figure 18] FIG. 13 is a heat map showing the stress distribution in the rib structure when the mirror portion is rotated back and forth around the vertical rotation axis Wy. [Figure 19] FIG. 23 is a diagram showing names of rib structures compared in FIGS. 20 to 22. [Figure 20] 11 is a comparison graph showing dynamic surface deformation for each level investigated by a simulation experiment. [Figure 21] 1 is a comparison graph showing experimental results of limiting mechanical run-out angles for each level. [Figure 22] FIG. 20 is a diagram showing the results of an experiment in which the limit swing angle and dynamic surface deformation were obtained by setting representative dimensions for the structures of each level in FIG. 19 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention is not limited to the illustrated embodiments, but includes various modifications within the scope of the technical concept of the present invention.

[0010] Figures 1 to 8 relate to a first embodiment of the optical deflector. Figures 9 and onwards relate to a second embodiment of the optical deflector. In the second embodiment, elements having a common configuration with the first embodiment or elements having substantially the same action and effect are denoted by the same reference numerals as the corresponding elements in the first embodiment, and descriptions thereof will be omitted as appropriate.

[0011] (light deflector) FIG. 1 is a schematic diagram of an optical deflector 10 according to the first embodiment, viewed obliquely from the front. The optical deflector 10 is manufactured as a MEMS device from an SOI (Silicon on Insulator) substrate. The SOI 64 (FIGS. 11A and 11B) of the embodiment typically has a five-layer laminated structure, and is arranged in order from top to bottom of the laminated structure, a first SiO2 layer (not shown), a second Si layer 64b, a third SiO2 layer 64c, a fourth Si layer 64d, and a fifth SiO2 layer (not shown). The top two layers (the first SiO2 layer and the second Si layer 64b) are called active layers, and the bottom three layers (the third SiO2 layer 64c, the fourth Si layer 64d, and the fifth SiO2 layer) are called BOX layers or handling layers.

[0012] For ease of explanation, the two main surfaces on either side of the thickness direction of the optical deflector 10 will be referred to as the front and back, respectively, on the side where the incident light La is incident and the opposite side, and the view from the front side will be referred to as the "front view" and the view from the back side will be referred to as the "rear view."

[0013] The overall configuration of the optical deflector 10 will be roughly described with reference to Fig. 1. Details of the overall configuration of the optical deflector 10 are as described in, for example, Japanese Patent Application Laid-Open No. 2012-203186 of the present applicant.

[0014] The optical deflector 10 may be installed in any device equipped as an optical scanner, such as a projector (including a picoprojector), a head-up display, an automobile headlamp with ADB (Adaptive Driving Beam), eyewear, an endoscopic device, a retinal projection examination device, a LiDAR, or the like.

[0015] The optical deflector 10 includes a mirror section 11, upper and lower torsion bars 12a, 12b, left and right inner actuators 13a, 13b, a movable frame 14, left and right outer actuators 15a, 15b, and a fixed frame 16. The inner actuators 13a, 13b and the outer actuators 15a, 15b are all piezoelectric actuators. The outer actuators 15a, 15b are composed of a plurality of piezoelectric cantilevers arranged in a meandering pattern and connected in series.

[0016] 1 are axes of a two-axis Cartesian coordinate system that intersect at right angles at the center of the reflecting surface of the mirror section 11. The axes Ax and Ay are set parallel to the horizontal and vertical directions of the fixed frame 16, which is rectangular when viewed from the front. The optical deflector 10 has a structure that is symmetrical with respect to the axis Ay.

[0017] Incident light La is emitted from a laser light source (not shown), enters the mirror section 11, is reflected by a reflecting surface on the front side of the mirror section 11, and is emitted from the mirror section 11 as scanning light Lb.

[0018] During operation of the optical deflector 10, a driving voltage is supplied to the inner actuator 13 (general term for the inner actuators 13a and 13b) and the outer actuator 15 (general term for the outer actuators 15a and 15b) from a driving device (not shown). This causes the mirror section 11 to rotate back and forth around the horizontal rotation axis Wx and the vertical rotation axis Wy (FIG. 2A) at a non-resonant frequency Fx and a resonant frequency Fy, respectively. Fx and Fy are, for example, 60 Hz and about 32 kHz, respectively. Note that the horizontal rotation axis Wx and the vertical rotation axis Wy coincide (overlap) with the axis Ax and the axis Ay when the mirror section 11 stops rotating back and forth, but tilt and become misaligned during the reciprocating rotation. Note that the center Ow remains stationary despite the reciprocating rotation of the mirror section 11.

[0019] Meanwhile, incident light La of a laser beam from a laser light source (not shown) is incident on the mirror unit 11 which rotates reciprocally around the horizontal rotation axis Wx and the vertical rotation axis Wy. As a result, scanning light Lb, which is reflected light of the incident light La, is emitted from the mirror unit 11 as a two-dimensional scanning beam.

[0020] 2A and 2B are perspective views of the inner structure 20 of the optical deflector 10 as viewed obliquely from the front and rear sides, respectively. The rib structure 24 provided on the mirror section 11 of this inner structure 20 is a first embodiment of the rib structure and is distinguished from a rib structure 25, which is a second embodiment and will be described later. The mirror section 11 is capable of reciprocating rotation around a horizontal rotation axis Wx and a vertical rotation axis Wy. The horizontal rotation axis Wx and the vertical rotation axis Wy are perpendicular to each other at the center Ow of the reflecting surface of the mirror section 11. The torsion bars 12a and 12b extend from both sides of the mirror section 11 along the vertical rotation axis Wy.

[0021] The structure of the optical deflector 10 is divided into an inner structure 20 and an outer structure (no reference number) that surrounds the inner structure 20. The inner structure 20 is composed of a mirror section 11, a torsion bar 12 (a collective term for the torsion bars 12a and 12b), an inner actuator 13, and a movable frame 14, and is a structure that contributes to rotating the mirror section 11 back and forth around a vertical rotation axis Wy at a resonant frequency Fy. In contrast, the outer structure is composed of an outer actuator 15 and a fixed frame 16, and is a structure that contributes to rotating the inner structure 20 back and forth around an axis Ax (FIG. 1) at a non-resonant frequency Fx.

[0022] The mirror section 11 includes a circular main body 22 and a rib structure 24 formed on the back side of the main body 22. The front side of the main body 22 is a reflective surface that reflects the incident light La and emits the scanning light Lb. Each torsion bar 12 is divided into an inner bar portion 32 on the mirror section 11 side and an outer bar portion 34 on the movable frame 14 side, with the boundary being the connection point with the inner actuator 13. The inner actuators 13a and 13b are connected to the inner circumference of the movable frame 14 via reinforcing connection portions 18a and 18b, respectively, on the horizontal rotation axis Wx.

[0023] (Mirror part) 3A is a rear view of the inner structure 20, FIG. 3B is a diagram showing by symbols the dimensions of each part of the mirror unit 11 as viewed from the rear side, and FIG. 3C is a cross-sectional view taken along the line F3C-F3C in FIG. 3A.

[0024] In FIG. 3A, the rib structure 24 is symmetrical with respect to the vertical rotation axis Wy and is symmetrical with respect to the horizontal rotation axis Wx. The rib structure 24 includes an elliptical rib 26 that occupies the center of the back surface of the mirror section 11, and equal-width protruding ribs 28a, 28b (first protruding ribs) that extend from the elliptical rib 26 along the vertical rotation axis Wy toward each torsion bar 12 with equal widths. The elliptical rib 26 and the equal-width protruding rib 28 (collectively referring to the equal-width protruding ribs 28a, 28b) protrude from the back surface of the main body 22 with an equal protruding amount (tr in FIG. 3C). The outer periphery of the elliptical rib 26 is defined by the contour line of a vertically long outer ellipse. The inner periphery of the elliptical rib 26 is defined by the contour line of a horizontally long inner ellipse. The inner periphery of the elliptical rib 26 is an elliptical recess 30 having a peripheral contour of the inner ellipse. The back surface of the main body 22 is exposed to the elliptical recess 30.

[0025] In FIG. 3B, the definitions of the symbols are as follows: D: Diameter of the circular body 22 (if the radius of the body 22 is R, then D = 2R.) a1, b1: The major and minor axis dimensions of the inner ellipse a2, b2: The dimensions of the minor and major axes of the outer ellipse wb: Width of the uniform width protruding rib 28

[0026] In FIG. 3C, the definitions of the symbols are as follows: tm: thickness of main body 22 tr: Protrusion dimension of the elliptical rib 26 from the back surface of the body 22

[0027] The relationships between the dimensions are set as follows: Note that the following dimensional values ​​are merely examples and are not limiting. a1>D / 2>b1 b1 <b2<D a1 <a2<D 2·tm <tr<3·tm 1mm <D<1.5mm 40μm <tm<50μm

[0028] (Torsion bar) 4A and 4B are front views of the inner bar portion 32 and the outer bar portion 34 of the torsion bar 12b, respectively. The definitions of the symbols are as follows. In the following, the horizontal axis direction and the vertical axis direction refer to the directions of the horizontal rotation axis Wx and the vertical rotation axis Wy, respectively. P1: Intersection point between the circumference of the main body 22 and the right edge of the inner bar portion 32 P2: The right end of the narrowest part of the inner bar portion 32 P3: Intersection point between the inner peripheral contour line of the inner actuator 13b and the right edge of the inner bar portion 32 P4: The point where the right edge of the outer bar portion 34 rises from the outer circumferential contour of the inner actuator 13b P5: Right end of the narrowest part of the outer bar portion 34 P6: The point where the right edge of the outer bar portion 34 rises from the inner peripheral contour line of the movable frame 14 (the horizontal axis positions of P4 and P6 are the same).

[0029] wi: The minimum width of the inner bar portion 32 in the horizontal direction wo: The minimum width of the outer bar portion 34 in the transverse direction ai1: The horizontal axis length between P1 and P2 ai2: The horizontal axis length between P2 and P3 ao: The horizontal axis length between P4 and P5 Li: Length along the vertical axis between P1 and P3 Lo: Length along the vertical axis between P4 and P6 bo: Length along the vertical axis between P5 and P6

[0030] Although this will be explained again later, to give an overview in advance, the following dimensional relationships and structure are stipulated: wb (Fig. 3B) ≦ wi + ai1. However, for ai1, see Fig. 4A. wi > wo. In each torsion bar 12, the side edge (Fig. 4A) of the inner bar portion 32 between the mirror portion 11 and the inner actuator 13 in the direction of the vertical rotation axis Wy, and the side edge (Fig. 4B) of the outer bar portion 34 between the inner actuator 13 and the movable frame 14 are both formed as continuous curves that convex inward in the width direction when viewed from behind. Furthermore, in the inner bar portion 32, the width on the mirror portion 11 side is narrower than that on the inner actuator 13 side (ai1 in Fig. 4A) <ai2)。

[0031] Comparative Example 1 5 is a perspective view of the mirror section 100 of Comparative Example 1 when viewed obliquely from the rear side. The mirror section 100 is described as a comparative example when describing the action and effect of the rib structure 24 of the mirror section 11 in FIG. 6 and subsequent figures.

[0032] The mirror section 100 comprises a circular main body 102 whose front side is a mirror surface, and a rib structure 104 formed on the back side of the main body 102. The rib structure 104 further comprises an equal-width elliptical rib 106, and expanding ribs 108a, 108b which are connected to both ends of the equal-width elliptical rib 106 in the vertical axis direction and which expand in the horizontal axis direction while protruding outward in the vertical axis direction.

[0033] The rib structure 104, like the rib structure 24, is symmetrical left-right and top-bottom with respect to the vertical rotation axis Wy and horizontal rotation axis Wx, respectively. The equal-width elliptical rib 106 and the expanding rib 108 (collectively referring to the expanding ribs 108a, 108b) extend with equal widths when viewed from the rear. The equal-width elliptical rib 106 has its major axis and minor axis aligned with the vertical rotation axis Wy and horizontal rotation axis Wx. The left and right protruding ends of the expanding rib 108 are connected to the protruding ends of each torsion bar that protrude in the left-right direction from the end of the mirror section 100 side.

[0034] In the mirror section 100, the length in the horizontal axis direction between the outer periphery of the equal-width elliptical rib 106 and the circumferential edge of the circular main body 102 is increased on the back surface of the main body 102, and this reduces the rigidity of the main body 102 outside the equal-width elliptical rib 106. If the minor axis of the equal-width elliptical rib 106 is lengthened to compensate for this, then the rigidity of the main body 102 inside the equal-width elliptical rib 106 will decrease.

[0035] (Effects of the first embodiment) 6A, 6B, 6C, and 6D are diagrams showing a heat map (FIG. 6A) of the thickness direction displacement (amount of deformation of dynamic surface deformation) of each part of the main body 22, the displacement amount at the coordinate position of the axis Ay=0 (FIG. 6B), the thickness direction displacement amount at the coordinate position of the axis Ax=150 (FIG. 6C), and the RMS heat map (FIG. 6D), respectively, under the conditions that the diameter of the main body 22 is 1.1 mm, the thickness (tm) of the main body 22 is 42.5 μm, the thickness (tr) of the rib structure 24 is 130 μm, and the mirror portion 11 is rotated back and forth around the vertical rotation axis Wy at a resonance frequency of 36 kHz and a deflection angle of the mirror portion 11 of 22° (= mechanical deflection angle ±11°). 7A, 7B, 7C, and 7D are diagrams showing test results for the same items as those in Fig. 6A, 6B, 6C, and 6D, respectively, when mirror section 100 is rotated back and forth under the same conditions as mirror section 11. Note that RMS stands for root mean square and corresponds to wavefront aberration (dynamic surface deformation).

[0036] 6A and other heat maps, it should be noted that, as can be seen from the shading of the scale on the right side, the areas where the dynamic surface deformation is 0.0 are gray, and the areas where the absolute value of the dynamic surface deformation is large are white and black. Also, the reason why the positive and negative dynamic surface deformations are opposite on one side and the other side of the horizontal rotation axis Wx is because the deflection direction of the mirror part 11 is opposite at the boundary of the horizontal rotation axis Wx.

[0037] X and Y in Figures 6A-6C and 7A-7C respectively refer to the coordinates of the horizontal rotation axis Wx and the vertical rotation axis Wy when the horizontal rotation axis Wx and the vertical rotation axis Wy are respectively set as orthogonal coordinate axes with the center Ow as the origin in Figure 2B. RMS and λ in Figures 6D and 7D respectively refer to the wavefront aberration and the wavelength of the incident light La.

[0038] 6A and 7A, it can be seen that the amount of displacement in the thickness direction, i.e., the deflection, of mirror portion 11 is significantly reduced relative to mirror portion 100. See the scale marks on the right of Figures 6A and 7A. The scale marks on the right of Figure 6A range from -0.22 to 0.22, whereas the scale marks on the right of Figure 7A range from -0.95 to 0.95.

[0039] 6B and 7B, in the optical deflector 10, the difference between the maximum and minimum displacement is 58 nm for the mirror section 11 and 282 nm for the mirror section 100, which indicates that the mirror section 11 is significantly smaller than the mirror section 100. The area surrounded by the dashed line in FIG. 6B indicates that the change in displacement with respect to the change in the coordinate of the horizontal axis is flattened near the center Ow. This means that despite the formation of the elliptical recess 30, the minor axis of the elliptical recess 30 has a sufficiently suppressed dimension, and the rigidity of the main body 22 near the center Ow on the horizontal rotation axis Wx is sufficiently maintained. On the other hand, the elliptical rib 26 is sufficiently widened along the horizontal rotation axis Wx, so that the rigidity of both ends of the main body 22 on the horizontal rotation axis Wx is strengthened.

[0040] In other words, the elliptical rib 26 sufficiently projects toward the periphery of the main body 22 of the mirror section 11, while forming an elliptical recess 30 on the inner peripheral side that is narrow in the vertical axis direction. This balances the rigidity of each part of the reflecting surface of the circular main body 22 during reciprocating rotation about the vertical rotation axis Wy, and as a result, dynamic deformation of the reflecting surface is sufficiently suppressed.

[0041] 6C and 7C, it can be seen that in the optical deflector 10, the difference between the maximum and minimum displacement amounts is 119 nm for the mirror section 11 and 838 nm for the mirror section 100, and that the mirror section 11 is significantly smaller than the mirror section 100. From the comparison between FIG. 6D and FIG. 7D, it can be seen that the RMS is λ / 15 (λ = 630 nm) for the mirror section 11 and λ / 2.2 for the mirror section 100, and that the mirror section 11 is significantly smaller than the mirror section 100, and that this embodiment has stronger rigidity at both the center and both ends. That is, in the heat map diagrams of FIG. 6D and FIG. 7D, the mirror section 11 is generally grayish and the difference in shading is small, whereas the mirror section 100 has a large difference in shading.

[0042] (Screen resolution) In SXGA (Super eXtended Graphics Array), θ op ·D≧60deg·mm and frame frequency ≧32kHz are required. op D=4 λ N x / π, and θ op , N x are the total optical scanning angle and the number of vertical scanning lines, respectively. In the embodiment, the diameter of the main body 22 is 1.3 mm, the deflection angle is 11.6°, the frame frequency is 36 kHz, λ (the wavelength of the incident light La, which is a laser light)=630 nm, and N x = (π θ op ·D) / (4·λ), the diameter D of the main body 22 is 1.3 mm, and θ op If we set 11.6°× 4 = 46.4, the embodiment can be used for SXGA.

[0043] In addition, for the inner bar portion 32 and outer bar portion 34 of the torsion bar 12, by adopting a side edge contour of a continuous curved line that maintains an inward convexity as described in Figures 4A and 4B, the diameter of the main body 22 was made 1.3 mm (the larger the diameter of the main body 22 of the mirror section 11, the higher the resolution). When the tests of Figures 6A to 6D were performed, it was confirmed that the maximum stress of the inner bar portion 32 and outer bar portion 34 of the inner actuator 13 was within the allowable value.

[0044] The reciprocating rotation of the mirror section 11 occurs due to the twisting of the torsion bars 12a and 12b, which generates stress in the torsion bar 12 (particularly the inner bar portion 32). If the strength of the location where the stress concentration occurs is weak, the torsion bar 12 will be destroyed.

[0045] The equal-width protruding ribs 28a, 28b are substantially rectangular parallelepiped-shaped, the length e1 (FIG. 3B) of the equal-width protruding ribs 28a, 28b is set to the outer periphery of the mirror portion 11, the thickness of the equal-width protruding ribs 28a, 28b is the same as the thickness tr of the elliptical rib 26, and the width wb of the equal-width protruding ribs 28a, 28b is formed to have the same dimensions as the width wi+ai1 of the torsion bar 12. However, the length e1 of the equal-width protruding ribs 28a, 28b is formed between the elliptical rib 26 and the torsion bars 12a, 12b, but is not allowed to protrude into the torsion bars 12a, 12b. This is because if the tips of the equal-width protruding ribs 28a, 28b protrude into the torsion bars 12a, 12b, the thickness of the torsion bar will be increased by that amount, making it difficult for the torsion bar to twist, and the swing angle of the mirror portion 11 will be reduced.

[0046] It is preferable that the width wb of the equal-width protruding rib 28 is equal to or smaller than the width wi+ai1 of the torsion bar 12. This is because, if the width wb of the equal-width protruding rib 28 becomes larger than the width wi+ai1 of the torsion bar 12, the outer periphery of the mirror part 11 becomes heavier due to the equal-width protruding ribs 28a, 28b, causing a problem that the deflection of the mirror part 11 increases due to the weight effect. Therefore, if the mirror part 11 needs to be stronger to resist the stress of the torsion bar 12, the thickness of the equal-width protruding ribs 28a, 28b can be increased, and conversely, the thickness can be reduced.

[0047] The inner bar portion 32 is formed such that the width wi+ai1 on the mirror portion 11 side is narrow and the width wi+ai2 on the inner actuators 13a and 13b side is wider, and the ai1 width on the mirror portion 11 side and the ai2 width on the inner actuators 13a and 13b side are formed as a side edge contour of a continuous curved line that maintains a convexity on the inside, and the length (Wy direction) of the side edge contour is formed such that the length of the ai2 width on the inner actuators 13a and 13b side is longer than the length of the ai1 width on the mirror portion 11 side. This allows the stress concentration generated by the twisting of the inner bar portion 32 to be shifted to the mirror portion 11 side (see FIG. 8). As a result, if the stress concentration is shifted to the mirror portion 11 side, the strength of the mirror portion side of the inner bar portion 32 is increased by the equal-width protruding ribs 28a and 28b, so that the inner bar portion 32 can withstand the stress concentration and is not destroyed by twisting.

[0048] The outer bar portions 34 may also have curved ends to reduce stress concentrations.

[0049] Second embodiment 9A and 9B are perspective views of an inner structure 50 provided in an optical deflector of the second embodiment, as viewed from the front and rear sides, respectively. The inner structure 50 is provided in place of the inner structure 20 provided in the optical deflector 10 of the first embodiment. For the sake of simplicity, in the description of the inner structure 50 from FIG. 9A onwards, elements that are substantially identical in structure or function to the elements of the inner structure 20 are given the same reference numerals as those given to the corresponding elements of the inner structure 20, and detailed descriptions thereof will be omitted.

[0050] The following description will focus on the torsion bars 52a, 52b, the rib structure 54, and the expansion ribs 58a, 58b of the inner structural portion 50, which are different from the elements of the inner structural portion 20. The inner structural portion 50 is formed symmetrically with respect to each of the horizontal rotation axis Wx and the vertical rotation axis Wy.

[0051] The mirror section 11 is supported by the movable frame 14 so as to be freely rotatable back and forth around the vertical rotation axis Wy via torsion bars 52a, 52b extending from the mirror section 11 along the vertical rotation axis Wy. The mirror section 11 has a disk-shaped main body 22 whose front side is a reflective surface, and a rib structure 54 formed on the back side of the main body 22 so as to protrude therefrom.

[0052] Fig. 10A is an enlarged rear view of the range including the mirror portion 11 in Fig. 9B. Fig. 10B is a diagram showing positions and the like in the rear view of Fig. 10A. Fig. 10C is a diagram showing a designated azimuth angle range 68 in the rear view of Fig. 10A. Fig. 10D is an enlarged rear view in which the rib structure 54 in Fig. 10A is replaced with a rib structure 55 as another embodiment. Figs. 11A and 11B are cross-sectional views taken along lines F11A-F11A and F11B-F11B in Fig. 10B, respectively.

[0053] 10A, the mirror section 11 and the torsion bar 52 (general term for the torsion bars 52a and 52b) are structured to be line-symmetrical with respect to each of the horizontal rotation axis Wx and the vertical rotation axis Wy in rear view. Each torsion bar 52 has horizontal extensions 60a and 60b that protrude linearly on both sides in the horizontal axis direction (direction of the horizontal rotation axis Wx) at the end on the mirror section 11 side by a predetermined length. Note that the horizontal extensions 60 (general term for the horizontal extensions 60a and 60b) extend parallel to the horizontal rotation axis Wx in the illustrated example, but may extend obliquely toward the mirror section 11.

[0054] The rib structure 54 has an elliptical rib 26 occupying the center of the back surface of the main body 22, and a pair of spreading ribs 58a, 58b (second protrusions) that protrude from both sides of the elliptical rib 26 in the vertical axis direction (the direction of the vertical rotation axis Wy) toward each torsion bar 52a, 52b. The paired shape of each spreading rib 58 (general term for spreading ribs 58a, 58b) spreads in the horizontal axis direction (the direction of the horizontal rotation axis Wx) as it moves away from Ow in the direction of the vertical rotation axis Wy, and then connects at its tip to the tip of the horizontal extension 60 of the torsion bar 52. The spreading rib 58 is bifurcated at the connection part with the horizontal extension 60, and each pair of spreading ribs 58 is formed in a shape like the left and right legs of a crab with scissors.

[0055] The joint between the expansion rib 58 and the lateral extension 60 is an overlapping portion in rear view, and shares the second-highest Si layer (Si 64b in FIG. 11A) among the five layers of the SOI 64 (FIGS. 11A and 11B). That is, this Si layer belongs to both the expansion rib 58 and the lateral extension 60. The joint on the expansion rib 58 side further includes SiO2 64c as the third layer of the SOI 64 and Si 64d as the fourth layer. Note that, in rear view, the front side is the BOX layer and the back side is the active layer, so the surface of the expansion rib 58 visible in FIG. 10A is the back surface of the fourth layer Si 64d.

[0056] In Fig. 10B, the definitions of the dimensional symbols are as follows. Note that explanations of the dimensional symbols already explained in Fig. 3B will be omitted. In Fig. 10B, in addition to the dimensional symbols, for the convenience of explaining the structure, an outer ellipse 56a, an inner ellipse 56b, an annular ellipse 62, etc. are also shown. Furthermore, in Fig. 10B and subsequent Figs., parts are appropriately shaded in black to clarify the rib structure when viewed from the back.

[0057] The definitions of the outer ellipse 56a, the inner ellipse 56b and the annular ellipse 62 are as follows. Outer ellipse 56a: An ellipse that defines the outer peripheral contour of the elliptical rib 26 Inner ellipse 56b: an ellipse that defines the inner peripheral contour of the elliptical rib 26 Annular ellipse 62: An annular ellipse whose inner and outer circumferences are approximated by the inner and outer contours of the expanding rib 58.

[0058] In FIG. 10B, the added dimension symbols are as follows: R: Radius of the body 22. The relationship is D=2R. a3: The dimension of the major axis of the inner periphery of the annular ellipse 62 a4: The dimension of the major axis of the outer periphery of the annular ellipse 62

[0059] Positions P11 to P16 are defined as follows. Hereinafter, the vertical axis and horizontal axis refer to the vertical rotation axis Wy and horizontal rotation axis Wx, respectively. Also, in FIG. 10B, these positions are only written in the upper annular ellipse 62, but they are defined similarly for the lower annular ellipse 62. Furthermore, in FIG. 10B, these positions are defined as positions to the left of the vertical axis (including positions on the vertical axis), but they can also be defined similarly as positions to the right.

[0060] P11: The closest point to the vertical axis on the line segment where the center line of the horizontal extension portion 60 passes through the expansion rib 58 in rear view P12: Intersection of the vertical axis and the outer ellipse 56a P13: The end point closer to the vertical axis of the two end points of the joining line of the root of the expansion rib 58 that joins the elliptical rib 26 on the outer ellipse 56a in the rear view. P14: The midpoint between P13 and P15 on the above connecting line P15: The end point of the connecting line that is farthest from the vertical axis P16: Intersection of the vertical axis and the inner ellipse 56b

[0061] The following dimension symbols are defined as follows: d1: Distance along the vertical axis between P11 and P12 d2: Distance along the vertical axis between P12 and P16 d11: Distance in the horizontal direction between the vertical axis and P14 d12: Distance in the horizontal direction between the vertical axis and P11

[0062] It is preferable that the following relationship exists: If C1 is half the length of a2, then (1 / 4)·C1≦d11≦(3 / 4)·C1. If C2 is the width of the narrowest part of the torsion bar 12 between the mirror portion 11 and the laterally extending portion 60 in the vertical axis direction, then d12>C2. Note that since the laterally extending portion 60 protrudes from the torsion bar 12 in the width direction, it is natural that d12>C2.

[0063] 10C, designated azimuth boundary lines 70a, 70b are set on each side in the horizontal direction on the back surface of the mirror unit 11 to define designated azimuth ranges 68a, 68b. Each designated azimuth boundary line 70 (a collective term for the designated azimuth boundary lines 70a, 70b) is defined as a straight line passing through P15 that are 180° apart clockwise from the center Ow. The designated azimuth ranges 68a, 68b are azimuth ranges determined between the designated azimuth boundary line 70a and the designated azimuth boundary line 70b on one side and the other side in the horizontal direction with respect to the vertical rotation axis Wy.

[0064] In each designated azimuth angle range 68, the horizontal rotation axis Wx is defined as an azimuth angle of 0°, and the clockwise and counterclockwise azimuth angles relative to the azimuth angle of 0° are defined as + and -, respectively. In each designated azimuth angle range 68, designated azimuth angle boundary lines 70a, 70b are azimuth angles of +α and -α, respectively. Therefore, both designated azimuth angle ranges 68a, 68b are defined as azimuth angle ranges between an azimuth angle of +α and an azimuth angle of -α, with the horizontal rotation axis Wx as an azimuth angle of 0° on each side of the vertical rotation axis Wy.

[0065] α is set, for example, to 10° to 75°. The set value is set as an azimuth angle corresponding to P13 where dynamic deformation outside the azimuth angle range of ±α on each side of the vertical rotation axis Wy is equal to or smaller than the allowable value in the heat map of the rib structure 54 in FIG.

[0066] In Fig. 10D, rib structure 54 in Fig. 10B is replaced with rib structure 55. Rib structure 54 has elliptical rib 26, while rib structure 55 has elliptical rib 27 instead of elliptical rib 26. The difference between elliptical rib 26 and elliptical rib 27 is that the outer periphery of elliptical rib 26 is formed on the periphery of outer ellipse 56a over the entire circumference, whereas the outer periphery of elliptical rib 27 is formed on the periphery of outer ellipse 56a within specified azimuth angle range 68, but is replaced by a recessed elliptical line 72 that is part of annular ellipse 62 (Fig. 10B) outside each specified azimuth angle range 68.

[0067] In rear view, the side edge of the base of the expansion rib 58 on the P13 side and the end of the designated azimuth angle range 68 form a single curved line. In other words, in rear view, the side edge line of the base of the expansion rib 58 on the P13 side and the side edge line of the end of the designated azimuth angle range 68 are connected by a smooth curve without any sharp corners at the joining point of the two.

[0068] The perimeter of the elliptical rib 27 outside the specified azimuth angle range 68 is not limited to the concave ellipse line 72. Various curved lines can be selected as the perimeter of the elliptical rib 27 outside the specified azimuth angle range 68 as long as the following two conditions are satisfied: the elliptical rib 27 does not protrude beyond the perimeter of the outer ellipse 56a, and outside the specified azimuth angle range 68, the elliptical rib 27 is curved convexly toward the center Ow with respect to the perimeter of the outer ellipse 56a.

[0069] In Fig. 11A and Fig. 11B, the SiO2 64a as the first layer (number 1) and the SiO2 64 as the fifth layer (number 5) have been removed from the original 64. The main body 22 has Si 64b as the second layer of the SOI 64. The SiO2 64a as the first layer of the SOI is peeled off, and a metal layer 66 as a mirror surface is formed on the front side of the main body 22. The elliptical rib 26 is composed of SiO2 64c as the third layer included in the BOX layer of the SOI 64 and Si 64d as the fourth layer, which are laminated on the back side of the main body 22. (a2-a1) / 2<(b2-b1) / 2. Note that (b2-b1) / 2=d1.

[0070] tv is the length between P12-P17. tw is the minimum width of the elliptical rib 26. tm is the thickness of the body 22. tr is the height of the elliptical rib 26 from the body 22. Example dimensions are tw=50 μm, tm=42.5 μm, and tr=130 μm.

[0071] Figure 12 shows three comparative examples of the mirror part. The three comparative examples are named PICO, PICO-E2, and PICO-E3 from left to right, and the level of dynamic surface deformation of the main body of the mirror part is referred to by these names. In Figure 12, the unit of the numerical values ​​of each part of PICO-E2 and PICO-E3 is μm.

[0072] The structure of the mirror section 101, which is a PICO, will be further explained. The mirror section 101 has a rib structure 105 instead of the rib structure 104 of the mirror section 100 in Fig. 5. The rib structure 105 has a laterally protruding rib 110 added to the rib structure 104. The laterally protruding rib 110 protrudes a predetermined amount from the equal-width elliptical rib 106 toward the periphery of the main body 102 along the horizontal axis (horizontal rotation axis Wx). The addition of the laterally protruding rib 110 enhances the rigidity of the main body 102 of the mirror section 101 compared to the mirror section 100.

[0073] Figures 13A and 13B show the dynamic surface deformation of the comparative example in Figure 12 in the form of a table and a graph, respectively. RMS stands for root mean square, and the smaller the value, the smaller the dynamic deformation of the main body reflecting surface of the mirror part. Laser light with λ (wavelength) = 633 nm was used as the irradiation light for the measurement.

[0074] Figure 14 is a grayscale image of a heat map of dynamic deformation of the main body (the reflective surface of the mirror part) in each rib structure. It should be noted in the heat map of Figure 14 that the main body of the mirror part is rotated 90° clockwise. Therefore, the left and right in Figure 14 correspond to the bottom and top in Figure 10A, respectively. In Figure 14, the horizontal rotation axis Wx and the vertical rotation axis Wy extend in the vertical and horizontal directions, respectively, and the values ​​on the horizontal and vertical axes indicate the distances (unit: μm) of the center Ow on the vertical rotation axis Wy and the horizontal rotation axis Wx, respectively.

[0075] It should be noted that, as can be seen from the grayscale scale on the right side of each heat map, the areas where the dynamic surface deformation is 0 are gray, and the areas where the absolute value of the dynamic surface deformation is large are white or black. In Fig. 14, the area where the RMS is 0 is on the vertical rotation axis Wy, and since the mirror surface of the main body swings in opposite directions on one side and the other side of the vertical rotation axis Wy, the RMS is smallest in the gray area, and the darker or lighter the area is, the larger the absolute value is, which means that the dynamic surface deformation is large.

[0076] The correspondence between each azimuth angle range of circled numbers 1 to 6 in the rib structure 105 in Fig. 14 and the designated azimuth angle boundary lines 70a and 70b in Fig. 10C will be described. The azimuth angle ranges of circled numbers 1 and 2 correspond to the azimuth angle range surrounded by the vertical rotation axis Wy and the designated azimuth angle boundary lines 70a and 70b on the upper side of the center Ow in Fig. 10C. The azimuth angle ranges of circled numbers 3 and 4 correspond to the azimuth angle range surrounded by the vertical rotation axis Wy and the designated azimuth angle boundary lines 70a and 70b on the lower side of the center Ow in Fig. 10C. The azimuth angle ranges of circled numbers 5 and 6 correspond to the designated azimuth angle range 68b ranging from +α to -α on the left side of the center Ow in Fig. 10C and the designated azimuth angle range 68a ranging from +α to -α on the right side.

[0077] Fig. 15 is a graph comparing the dynamic surface deformation for the rib structures in Fig. 14. Rib structures 24, 54, and 105 correspond to those in Fig. 14. Note that the resonant frequency is 36 kHz, the mechanical deflection angle is 11°, and the effective diameter of the mirror portion 11 (reflection surface) is 1.06 mm. It can be seen from Figs. 14 and 15 that the dynamic surface deformation is smallest for the rib structures 24, 54, and 105.

[0078] FIG. 16 is a graph comparing the mechanical runout angles of the rib structures in FIG. 14. The rib structures 24, 54, and 105 correspond to those in FIG. 14. The resonant frequency is 36 kHz, and the number of samples is 8 for the rib structure 54 and 2 for the rib structures 105 and 24. The values ​​may vary slightly for each sample. The mechanical runout angle is 1 / 2 the reciprocating rotation angle when the torsion bar 12 is damaged and the mirror section 11 can no longer reciprocate as the drive voltage of the inner actuator 13 is gradually increased, that is, the reciprocating rotation angle of the mirror section 11 around the vertical rotation axis Wy is increased. From FIG. 16, it can be seen that the mechanical runout angles are 105, 54, and 24 in order from best to worst.

[0079] FIG. 17 is a heat map of stress distribution investigating the cause of low mechanical runout angle in the rib structure 24. The equal-width protruding rib 28b has a two-layer structure of SiO2 64c and Si64d of SOI64 from the main body 22 side. This heat map was taken when the mirror part 11 was rotated back and forth around the vertical rotation axis Wy. From FIG. 17, it can be seen that stress concentration occurs in the SiO2 64c of the equal-width protruding rib 28b when the mirror part 11 rotates back and forth. From this, it can be seen that the stress concentration in the SiO2 64c increases the material limit stress of SiO2, and when the limit is exceeded, a crack occurs in the SiO2 64c first, and then the crack starts to cause destruction of Si64d, destroying the torsion bar. It can be seen that the material limit stress of SiO2 is an obstacle to increasing the mechanical runout angle.

[0080] 16, the mechanical run-out angle is high in the rib structure 105 with the expanding rib 108. Therefore, in order to achieve both suppression of dynamic surface deformation of the reflecting surface and an increase in the mechanical run-out angle, it is found that the rib structure 25 in which the uniform-width protruding rib 28 of the rib structure 24 is replaced with the expanding rib 108 of the mirror section 100 and the uniform-width elliptical rib 106 of the mirror section 100 is replaced with the elliptical rib 26 of the rib structure 24 is advantageous in terms of achieving both.

[0081] 18 is a heat map showing the stress distribution in the rib structures 54, 55 when the mirror portion 11 is rotated back and forth around the vertical rotation axis Wy. It can be seen that in the rib structures 54, 55, the stress in the joining end region of the torsion bar 52 to the mirror portion 11 is sufficiently distributed.

[0082] Fig. 19 is a diagram showing the names of the rib structures compared in Figs. 20 to 22. Numerical values ​​indicate the dimensions of corresponding parts (unit: µm). Levels A and C are provided with rib structure 54, and level B is provided with rib structure 55. Level PICO is provided with rib structure 105. Level with equal width protrusion is provided with rib structure 24.

[0083] Figure 20 is a comparison graph in which the dynamic surface deformation for each level was investigated by a simulation experiment. Note that in this experiment, the same as in the case of Figure 15, the resonance frequency was 36 kHz, the mechanical deflection angle was 11°, and the effective diameter of the mirror part 11 was 1.06 mm. It can be seen that the PICO level had large dynamic surface deformation, whereas the other levels had sufficiently reduced dynamic surface deformation.

[0084] FIG. 21 is a comparative graph in which the limit mechanical runout angle for each level was examined by experiment. Note that the limit mechanical runout angle is used synonymously with the mechanical runout angle described above. FIG. 21 shows that the equal-width protrusion level (rib structure 24) had low dynamic surface deformation (FIG. 20), but the limit mechanical runout angle was low. For this reason, if the equal-width protrusion level (rib structure 24) is used only in applications that do not require a large limit mechanical runout angle, it is possible to suppress dynamic surface deformation while still adequately achieving the intended purpose.

[0085] Figure 22 is a diagram showing the experimental results of determining the limit (mechanical) deflection angle and dynamic surface deformation (wavefront aberration) by setting representative dimensions for the structure of each level in Figure 19. It can be seen that the equal-width protrusion level has a low limit (mechanical) deflection angle, but small dynamic surface deformation. It can be seen that the PICO level does not sufficiently suppress dynamic surface deformation. It can be seen that levels A and C provide sufficient suppression of both the limit (mechanical) deflection angle and dynamic surface deformation.

[0086] As described above, in the first embodiment of the present invention, it is possible to suppress dynamic surface deformation of the reflecting surface of the mirror section 11. In the second embodiment of the present invention, in addition to suppressing dynamic surface deformation of the reflecting surface of the mirror section 11, it is also possible to increase the mechanical deflection angle. [Explanation of symbols]

[0087] 10 optical deflector, 11 mirror portion, 12 torsion bar, 13 inner actuator, 14 movable frame (support member), 22 main body, 24, 54, 55 rib structure, 26 elliptical rib, 28a, 28b equal-width protruding ribs (first protruding ribs), 30 elliptical recess, 32 inner bar portion, 34 outer bar Part, 52a, 52b...torsion bar, 56a...outer ellipse, 56b...inner ellipse, 58a, 58b...expansion rib (second protruding rib), 60a, 60b...lateral extension portion, 62...auxiliary elliptical ring, 68a, 68b...specified azimuth angle range, 72...concave ellipse line (curved line), Ow...center, Wx...horizontal rotation axis, Wy...vertical rotation axis.

Claims

1. A support member; a mirror portion having a circular main body with a reflective surface and a rib structure formed on a rear surface of the main body; a pair of torsion bars extending along the rotation axis on both sides of the mirror section in the direction of the rotation axis and connected to the support member and the mirror section at both ends; an actuator coupled to a side edge of each torsion bar for rotating each torsion bar back and forth about the rotation axis; An optical deflector comprising: The rotation axis is defined as a vertical axis, and an axis perpendicular to the vertical axis at the center of the mirror portion is defined as a horizontal axis, an outer ellipse having a major axis and a minor axis respectively lying on the vertical axis and the horizontal axis when viewed from behind the mirror portion, and an inner ellipse located inside the outer ellipse and having a major axis and a minor axis respectively lying on the horizontal axis and the vertical axis, defining a specified azimuth angle range within a range of ±α on each side of the horizontal axis direction relative to the center, with the azimuth angle on each side being 0° on the horizontal axis; The rib structure includes an elliptical rib formed on the inside of the periphery of the outer ellipse, including on the periphery of the outer ellipse; An optical deflector, wherein the outer periphery of the elliptical rib is formed on the circumference of the outer ellipse at least in each specified azimuth angle range, and the inner periphery is formed on the circumference of the inner ellipse.

2. The lengths of the major and minor axes of the inner ellipse are a1 and b1, respectively, the lengths of the major and minor axes of the outer ellipse are b2 and a2, respectively, and the radius of the body is R.

2. The optical deflector according to claim 1, wherein a1>R and b1<R.

3. 3. The optical deflector according to claim 2, wherein a2>a1>R.

4. 4. The optical deflector according to claim 3, wherein b2-b1>a2-a1.

5. An optical deflector as claimed in any one of claims 1 to 4, wherein the rib structure includes a first protruding rib protruding from the elliptical rib along the longitudinal axis on both sides of the elliptical rib in the direction of the longitudinal axis toward the periphery of the body with an equal width and a length not exceeding the periphery of the body.

6. 6. The optical deflector according to claim 5, wherein the width of the first protruding rib is equal to or smaller than the width of the torsion bar when viewed from the rear.

7. 6. The optical deflector according to claim 5, wherein each torsion bar has a width between the mirror section and the actuator in the longitudinal direction, the width being narrower on the mirror section side than on the actuator side.

8. each torsion bar has a side edge between the mirror portion and the actuator in the longitudinal axis direction and a side edge between the actuator and the support member, the side edge being formed by a continuous curve that is convex toward an inner side in the width direction when viewed from the rear; 8. The optical deflector according to claim 7, wherein the continuous curve of the torsion bar on the mirror section side is formed to have a narrower width than the continuous curve of the torsion bar on the actuator side.

9. Each torsion bar has a horizontal extension portion that protrudes in the horizontal axis direction from a position that is a predetermined distance away from the main body of the mirror portion in the vertical axis direction, An optical deflector as described in any one of claims 1 to 4, wherein the rib structure has a second protruding rib that is connected to the elliptical rib on the outer ellipse at its root, the end of the axial direction side of the connection line between the root and the outer ellipse is located on the boundary line of the specified azimuth angle range, and protrudes from the root and is connected to the horizontal extension portion at its tip.

10. 10. The optical deflector of claim 9, wherein the outer periphery of the elliptical rib extends along a perimeter of the outer ellipse in an azimuth angle range outside the specified azimuth angle range.

11. 10. The optical deflector according to claim 9, wherein the outer periphery of the elliptical rib is formed by a curved line that is curved convexly from a circumferential line of the outer ellipse toward the inner ellipse in an azimuth angle range outside the specified azimuth angle range.

12. The curved line is a perimeter of a predetermined ellipse whose minor axis is on the longitudinal axis, The optical deflector according to claim 11 , wherein a side edge of the base of each of the second protruding ribs on the boundary line side extends along a periphery of the predetermined ellipse in rear view.

13. On the vertical axis, the length between the periphery of the main body and the outer periphery of the elliptical rib is d1, the length between the outer periphery and the inner periphery of the elliptical rib is d2, 1 / 2 the length of the minor axis of the inner ellipse is d3, and the radius of the main body is R.

10. The optical deflector according to claim 9, wherein 0.1≦d1 / R≦0.3, 0.0.2≦d2 / R≦0.4, d3 / R≧0.4, and (d1+d2+d3) / R=1.

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