Light deflector

A light deflector 1 includes a reflector (2), inner piezoelectric actuators (4), an inner frame (5), outer piezoelectric actuators (6), and an outer frame (7). The reflector (2) is oscillated about a first axis Ua and a second axis Ub by the inner piezoelectric actuators (4) and the outer piezoelectric actuators (6), respectively. Formed on the rear surface of the light deflector 1 is a projecting rib (52), which projects from an encircling rib (51) of the inner frame (5) and reaches a corner portion (36) of a distal end portion of a piezoelectric cantilever (13a). A vertical side (22b) has an outer recess (35). The outer recess (35) extends along the projecting rib (52) in a portion of the distal end side of the piezoelectric cantilever (13a).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light deflector that outputs incident light as scanning light about two axes.

2. Description of the Related Art

As a light deflector of a Micro Electro Mechanical System (MEMS), there has been known a light deflector which oscillates a reflector about two axes by a piezoelectric actuator and deflects incident light by the reflection of the reflector and then outputs the incident light as two-dimensional scanning light (e.g. Japanese Patent Application Laid-Open No. 2017-207630 and Japanese Patent Application Laid-Open No. 2015-184590).

In the light deflector of the MEMS described in Japanese Patent Application Laid-Open No. 2015-184590, an encircling rib is formed on the rear surface side of an inner frame that supports a reflector through torsion bars, and a projecting rib, which projects from the encircling rib and further projects into an outer piezoelectric actuator, is formed on the rear surface side of the outer piezoelectric actuator.

In the light deflector described in Japanese Patent Application Laid-Open No. 2015-184590, the joining strength between the inner frame and the outer piezoelectric actuator has been increased by the encircling rib and the projecting rib, but an increase of a limit deflection angle of the reflector is insufficient. The limit deflection angle refers to a deflection angle at which any one part of the light deflector is damaged, making it difficult to further increase the deflection angle, in the process of gradually increasing the deflection angle of the reflector when the drive voltage of the piezoelectric actuator is gradually increased at a reference frequency while testing the light deflector.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light deflector capable of increasing the limit deflection angle of a reflector while securing the strength of joining of an outer piezoelectric actuator to an inner frame.

A light deflector according to the present invention includes:

a reflector which reflects light incident upon a front surface side;

an inner frame which surrounds the reflector;

an outer frame which surrounds the inner frame;

a pair of torsion bars which extend out of the reflector in the direction of a first axis out of the first axis and a second axis, which intersect with each other at right angles at the center of the reflector;

an inner piezoelectric actuator which is interposed between the inner frame and the pair of torsion bars and which oscillates the reflector about the first axis through the pair of torsion bars; and

an outer piezoelectric actuator which has a plurality of piezoelectric cantilevers connected by a meander pattern configuration, in which a first piezoelectric cantilever and a last piezoelectric cantilever in a configuration order from the inner frame side to the outer frame are connected to the inner frame and the outer frame, respectively, and which oscillates the inner frame about the second axis,

wherein an encircling rib is formed on the rear surface of the inner frame such that the encircling rib encircles the inner frame,

a projecting rib is formed on the rear surface of a distal end portion of the first piezoelectric cantilever such that the projecting rib projects from the encircling rib and extends toward the area of a corner portion of the first piezoelectric cantilever, the area of the corner being adjacent to a second piezoelectric cantilever,

the first piezoelectric cantilever has an outer recess which is concave toward the inner frame on one vertical side adjacent to the second piezoelectric cantilever, and

the outer recess extends along the projecting rib at the corner portion in a part on the distal end side of the first piezoelectric cantilever.

According to the present invention, the encircling rib and the projecting rib provide a large force of joining of the outer piezoelectric actuator to the inner frame. On the other hand, a step is created on the rear surface of the distal end portion of the first piezoelectric cantilever due to the projecting rib, and stress tends to be concentrated on the step. The outer recess effectively releases the stress attributable to the step, thereby reducing damage in the vicinity of the step of the distal end portion of the first piezoelectric cantilever. This makes it possible to increase the limit deflection angle of the reflector.

Preferably, in the light deflector according to the present invention, the projecting end of the projecting rib is directed toward the distal end of the first piezoelectric cantilever.

With this arrangement, stress in the vicinity of the outer recess can be lessened, thus enabling a further increase of the limit deflection angle of the reflector.

Preferably, in the light deflector according to the present invention, the other vertical side of the first piezoelectric cantilever that is adjacent to the inner frame has an inner recess that is concave toward the second piezoelectric cantilever in the distal end portion.

With this arrangement, the combination of the outer recess and the inner recess makes it possible to enhance the damage control effect in the distal end portion of the first piezoelectric cantilever.

Preferably, in the light deflector according to the present invention, the inner frame is formed to have an annular shape or an annular shape that is longer in the direction of the first axis than in the direction of the second axis.

Especially when the inner frame is formed to have an annular shape that is longer in the direction of the first axis than in the direction of the second axis, the stress that occurs, while the light deflector is in operation, at a portion where the piezoelectric cantilever of the outer piezoelectric actuator is joined to the inner frame can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Overall Configuration of the Light Deflector)

FIG. 1is a front view of a light deflector1. The front of the light deflector1refers to the surface (the surface on the front surface side) on which various types of layers are deposited when the light deflector1as a MEMS is fabricated, using a silicon on insulator (SOI) board40(FIGS. 3A and 3B) as a substrate. Further, the rear surface of the light deflector1refers to the surface on the rear side in the light deflector1on a flat board.

The light deflector1is configured to be laterally symmetrical in a front view, and includes, in the arrangement order from a center O of the light deflector1to the outside, a reflector2, torsion bars3, inner piezoelectric actuators4, an inner frame5, outer piezoelectric actuators6, and an outer frame7. The torsion bars3are disposed in a paired manner, one each on the upper side and the lower side with respect to the reflector2in a front view. The inner piezoelectric actuators4and the outer piezoelectric actuators6are disposed in the paired manner, one each on the left side and the right side with respect to the reflector2in the front view.

For the convenience of the explanation of the configuration of the light deflector1, a three-axis coordinate system, in which axes are mutually orthogonal at an origin, will be defined. The light deflector1includes movable elements that are displaced as the inner piezoelectric actuators4and the outer piezoelectric actuators6are driven; however, the position of the center O of the light deflector1remains unchanged. The center O of the light deflector1also provides the centers of the reflector2, the inner piezoelectric actuators4, the inner frame5, and the outer piezoelectric actuators6, and the centers also remain immovable. The origin of the three-axis coordinate system is set at the immovable center O.

An X-axis, a Y-axis and Z-axis intersect at right angles at the center O. The X-axis and the Y-axis are set in parallel to the long sides and the short sides, respectively, of the rectangular outer frame7. The Z-axis is set in parallel to the direction of the thickness of the tabular light deflector1.

Outgoing light from a light source (e.g. a laser light source), which is not illustrated, enters the center O of the reflector2. The center O is the center of not only the reflector2but also the center of each of the inner frame5and the outer frame7. The inner frame5surrounds the reflector2and the torsion bars3. The outer frame7surrounds the inner frame5.

The light incident upon the center O is deflected in a direction based on the direction of the normal line of the reflector2at the center O, and exits from the light deflector1. When the inner piezoelectric actuators4and the outer piezoelectric actuators6are being driven, the reflector2oscillates about a first axis Ua and a second axis Ub, so that the deflected light from the light deflector1will be two-dimensional scanning light. The first axis Ua and the second axis Ub coincide with the Y-axis and the X-axis, respectively, while the light deflector1is not in operation, i.e. while the inner piezoelectric actuators4and the outer piezoelectric actuators6are not being driven.

The torsion bars3extend along the first axis Ua from the reflector2and are joined to the inner circumference of the inner frame5. The torsion bars3are joined, at the middle thereof to the upper and lower end portions of the left and right inner piezoelectric actuators4. In the present embodiment, the shape formed by the left and right inner piezoelectric actuators4joined to each other and the shape of the inner frame5are longer in the Y-axis direction like the track of an athletic stadium in a front view.

The outer piezoelectric actuators6have a plurality of (five in the light deflector1, which is illustrated) cantilevers13which are connected in a meander pattern configuration, the longitudinal direction thereof being in parallel to the Y-axis. For individual identification, each of the plurality of piezoelectric cantilevers13is identified by the number assigned based on the arrangement order starting from the inner frame5.

The outer piezoelectric actuators6are interposed between the inner frame5and the outer frame7. In the outer piezoelectric actuators6, the lengths in the Y-axis direction (the lengths in the longitudinal direction of the piezoelectric cantilevers13) of a first piezoelectric cantilever13and a last-numbered piezoelectric cantilever13in the arrangement order of the plurality of piezoelectric cantilevers13placed from the inner frame5to the outer frame7in the outer piezoelectric actuators6are set to be substantially half the lengths of the remaining piezoelectric cantilevers13, and the first piezoelectric cantilever13and the last-numbered piezoelectric cantilever13are connected to the inner frame5and the outer frame7, respectively. InFIG. 1, for the convenience of explanation to be given later, the first and a second piezoelectric cantilevers13in the arrangement order are illustrated with reference numerals13aand13b, respectively, in addition to reference numeral13. Roots19are the end edges that join the piezoelectric cantilevers13ato the inner frame5.

Electrode pads15are formed on the surfaces of the left and right side portions of the outer frame7. When the light deflector1is sealed in a package (not illustrated), the electrode pads15are connected to corresponding terminals in the package through bonding wires (not illustrated). The electrode pads15are connected to corresponding electrodes of a piezoelectric structure47(FIGS. 3A and 3B) of the inner piezoelectric actuators4and the outer piezoelectric actuators6through the internal wiring of a wiring layer in the light deflector1.

[Overall Operation of the Light Deflector]

Drive voltages of a first frequency (e.g. 15 to 25 kHz) are supplied in reverse phases to the left and right inner piezoelectric actuators4from the left and right electrode pads15. The inner piezoelectric actuators4are interposed between the torsion bars3and the inner frame5. The reflector2is oscillated about the first axis Ua at the first frequency by twisting the torsion bars3. Resonance is utilized for the oscillation.

Drive voltages of a second frequency (e.g. 60 Hz), which has a reverse phase relationship between odd-numbered (a first, a third and a fifth) piezoelectric cantilevers13and even-numbered (a second and a fourth) piezoelectric cantilevers13in the foregoing arrangement order, are supplied to the outer piezoelectric actuators6from the left and right electrode pads15. This causes odd-numbered piezoelectric cantilevers13and the even-numbered piezoelectric cantilevers13to curve in the opposite directions in the Z-axis direction. The outer piezoelectric actuators6oscillate the inner frame5at the second frequency about the X-axis at an oscillation angle based on the total amount of the amounts of rotation of the piezoelectric cantilevers13about the second axis Ub. As the inner frame5oscillates about the X-axis, the reflector2oscillates about the second axis Ub at the second frequency. The oscillation of the reflector2about the second axis Ub does not utilize resonance, and the second frequency is lower than the first frequency.

The light that enters the center O of the reflector2from the light source is deflected in the direction according to the oscillation angle of the reflector2about the first axis Ua and the second axis Ub, reflected on the reflector2, and exits. The direction of the deflection changes from moment to moment according to the changing deflection angle of the reflector2while the light deflector1is in operation. As a result, the reflected light of the reflector2turns into scanning light that scans about the second axis Ub at the second frequency while scanning about the first axis Ua at the first frequency.

(Configuration of the Distal End Portion of the Piezoelectric Cantilever)

FIG. 2is an enlarged view of the distal end portion of the piezoelectric cantilever13aofFIG. 1, which is observed from the rear surface side.FIGS. 3A and 3Bare related to the section of the distal end portion,FIG. 3Abeing a sectional view taken along line3A-3A ofFIG. 2, andFIG. 3Bbeing a sectional view taken along line3B-3B ofFIG. 2.

InFIG. 2, andFIGS. 4A to 4CandFIGS. 5A and 5B, which will be discussed later, the outlines of an encircling rib51and a projecting rib52and the visible outlines of the inner frame5and the piezoelectric cantilever13a, which are viewed from the rear surface, do not overlap, and a fixed-width interval is provided between the two in the drawings. However, the interval is shown in order to avoid the difficulty in viewing due to the overlapping of the two, and in the actual structure, the two overlap when viewed from the rear surface.

Referring toFIG. 2, the inner frame5is joined to the outer peripheries of the inner piezoelectric actuators4by an overhanging part17that extends toward the inner piezoelectric actuators4in the X-axis direction. Marking lines C1and C2are straight lines that overlap the side edges on both sides in the Y-axis direction of the overhanging part17observed in the rear surface view. The X-axis coincides with the centerlines of the marking lines C1and C2.

A marking line C3is drawn along the boundary line between the inner frame5and the piezoelectric cantilever13a, and corresponds to the root19at which the piezoelectric cantilever13ais joined to the inner frame5. The root19exists within a range that overlaps the overhanging part17in the Y-axis direction. In the following description, in the piezoelectric cantilever13a, the portion on the negative side (the lower side inFIG. 2) relative to the marking line C1in the Y-axis direction will be referred to as “the distal end portion” of the piezoelectric cantilever13a.

The piezoelectric cantilever13ahas a vertical side22aadjacent to the inner frame5, a vertical side22badjacent to the piezoelectric cantilever13b, and a horizontal side25that extends to the root19in the X-axis direction from the vertical side22b. The piezoelectric cantilever13ahas a proximal end and a distal end in the longitudinal direction (the Y-axis direction), the end thereof joined to the piezoelectric cantilever13bcorresponds to the proximal end of the piezoelectric cantilever13a, and the end thereof adjacent to the horizontal side25corresponds to the distal end.

A corner30of the piezoelectric cantilever13aprovides the boundary between the vertical side22band the horizontal side25. A corner portion36is defined by the vertical side22band the horizontal side25and exists as the corner portion of the piezoelectric cantilever13aon the piezoelectric cantilever13bside. The corner30exists, in the corner portion36, on the outline of the piezoelectric cantilever13a.

The position of the corner30is set at a position where a tangent line passing the corner30inclines 45 degrees with respect to X-axis and Y-axis when the corner portion36is viewed from the Z-axis direction.

An outer recess35is formed in a part of the vertical side22bin the distal end portion closer to the marking line C2than the marking line C1(e.g. between the second axis Ub and the marking line C2in the Y-axis direction). The outer recess35is bisected to a proximal portion and a distal portion on the basis of the definition of the distal side and the proximal side in the longitudinal direction of the piezoelectric cantilever13a. In the distal end portion (the lower portion of the outer recess35inFIG. 2), the outer recess35extends along the contour of the projecting rib52in the corner portion36. In the proximal end portion (the upper portion of the outer recess35inFIG. 2), the outer recess35extends away from the projecting rib52. A projecting end55of the projecting rib52projects from the encircling rib51and extends to the corner portion36. More specifically, the projecting end55extends beyond the marking line C2and reaches the corner30at the distal end of the corner portion36as an area.

Referring toFIGS. 3A and 3B, a description will be given of the laminated structure of the distal end portion of the piezoelectric cantilever13a.

InFIGS. 3A and 3B, the light deflector1uses an SOI board40as the substrate. The laminated structure of the SOI board40includes an active layer41, a BOX layer42and a support layer43, which are deposited from the front surface side. The active layer41and the support layer43are composed of silicon (Si), and the BOX layer42is composed of silicon dioxide. Technically, the two surfaces, namely, the front surface and the rear surface, of the SOI board40are both coated with thin oxide film layers (not illustrated).

InFIG. 2andFIGS. 3A and 3B, the encircling rib51is formed on the rear surface side of the inner frame5. The encircling rib51encircles along the frame shape of the inner frame5. The projecting rib52continues to the encircling rib51and enters into the distal end portion of the piezoelectric cantilever13abeyond the root19from the encircling rib51.

The encircling rib51and the projecting rib52are formed by etching from the rear surface side of the SOI board40in the process of fabricating the light deflector1. Referring toFIGS. 3A and 3B, the two-dot chain line continuing from the lower end of the support layer43is given as a reference to indicate the original thickness of the support layer43before being cut away. The support layer43of the outer frame7(FIG. 1) is not etched, so that the lower surface of the support layer43of the outer frame7coincides with the position of the lower surface of the two-dot chain line inFIGS. 3A and 3Bin the Z-axis direction.

On the rear surface of the distal end portion of the piezoelectric cantilever13a, the portion where the encircling rib51and the projecting rib52exist protrudes from the rear surface of the active layer41, because not all the support layer43is cut away. On the rear surface, the portion where the encircling rib51and the projecting rib52are not formed exposes the rear surface of the active layer41, because the BOX layer42and the support layer43are completely removed.

As a result, the rear surface of the distal end portion of the piezoelectric cantilever13aincludes an area without rib Fa, which has a small amount of protrusion toward the rear surface due to the absence of the projecting rib52, and an area with rib Fb, which has a large amount of protrusion toward the rear surface due to the presence of the encircling rib51and the projecting rib52. A step occurs at the boundary between the area without rib Fa and the area with rib Fb. Further, the stress acting on the piezoelectric cantilever13atends to be concentrated on the area in the vicinity of the step of the distal end portion of the piezoelectric cantilever13awhile the light deflector1is being operated.

The inner recess37is formed in the end portion on the distal end side of the piezoelectric cantilever13aof the vertical side22a. The inner recess37is concave toward the piezoelectric cantilever13bin the X-axis direction. More specifically, the inner recess37is formed at a position between the marking line C1and the marking line C2and closer to the marking line C1in the Y-axis direction. The direction from the inner recess37toward the outer recess35is set along the direction of a stress propagation direction Tf (FIGS. 5A and 5B).

COMPARATIVE EXAMPLES

FIGS. 4A to 4CandFIGS. 5A and 5Billustrate the structures of the distal end portions of various types of comparative examples provided for comparison with the distal end portion of the piezoelectric cantilever13a. The outer recess35is omitted in the distal end portions of the comparative examples100,110and120inFIG. 4AtoFIG. 4C. In the comparative examples130and140ofFIG. 5AandFIG. 5B, the inner recess37is omitted, although at least either the outer recess35or the projecting end55directed toward the distal end side is provided.

Referring toFIGS. 4A to 4BandFIGS. 5A and 5B, the stress propagation direction Tf indicates the propagation direction of the stress that propagates to the distal end portion from the inner frame5when the normal line of the center O of the reflector2coincides with the Z-axis in the period during which the reflector2oscillates about the first axis Ua and the second axis Ub by being driven by the inner piezoelectric actuators4and the outer piezoelectric actuators6. The first axis Ua and the second axis Ub coincide with the Y-axis and the X-axis, respectively, when the normal line of the center O of the reflector2coincides with the Z-axis.

The stress propagation direction Tf is inclined with respect to the X-axis rather than being parallel to the X-axis. More specifically, the stress propagation direction Tf inclines at a predetermined angle on a negative side in the Y-axis direction from the proximal end to the distal end.

The distal end portion of a comparative example100ofFIG. 4Adiffers from the distal end portion of the light deflector1in the following two aspects: (1) the vertical side22bis formed by a straight line that is parallel to the Y-axis over the full length, while the horizontal side25is formed by a straight line that is parallel to the X-axis over the full length, and the intersection angle of the vertical side22band the horizontal side25is a right angle; and (2) the projecting rib52projects in parallel to the X-axis at a fixed width over the full length.

The distal end portion of a comparative example110ofFIG. 4Bdiffers from the distal end portion of the comparative example100in the following two aspects: (1) the horizontal side25is formed by an inclined line along the stress propagation direction Tf; and (2) the width of the projecting rib52in the Y-axis direction gradually increases toward the piezoelectric cantilever13b.

The distal end portion of a comparative example120ofFIG. 4Cdiffers from the distal end portion of the comparative example100in the following two aspects: (1) the projecting rib52is omitted; and (2) the vertical side22ahas an inner recess37which is similar to that of the distal end portion of the light deflector1.

The distal end portion of a comparative example130ofFIG. 5Adiffers from the distal end portion of the light deflector1in the following three aspects: (1) the outer recess35of the vertical side22bis omitted; (2) the horizontal side25is formed of a straight line inclined to the positive side in the Y-axis direction toward the corner30from the root19; and (3) the projecting end55of the projecting rib52is directed to the proximal end of the piezoelectric cantilever13a.

The distal end portion of a comparative example140ofFIG. 5Bdiffers from the distal end portion of the light deflector1in that the inner recess37is omitted.

Table 1 below indicates the stress values of the root19and an anti-root in each distal end portion of the light deflector1and the comparative example100to the comparative example140. The anti-root refers to a portion that extends along the piezoelectric cantilever13bin the distal end portion of the piezoelectric cantilever13a. In the distal end portion of the piezoelectric cantilever13a, the two sides in the X-axis direction are formed of the root19and the anti-root.

In Table 1, larger values mean higher stress, although the unit of stress is not shown.

The comparison in stress between the comparative example100and the comparative example110shows that increasing the width of the piezoelectric cantilever13ain the Y-axis direction, as in the comparative example110, makes it possible to improve, i.e. reduce, the stress of the root19accordingly. However, the stress of the anti-root inconveniently increases.

The comparison in stress between the comparative example100and the comparative example120shows that omitting the projecting rib52and setting the vertical side22band the horizontal side25to be orthogonal to each other, as in the comparative example120, improves the stress of the anti-root. However, it is also shown that the stress of the anti-root19is not yet sufficiently lower, leaving room for improvement.

The comparison in stress between the comparative example130and the comparative example140shows that the stress of the anti-root can be significantly improved by directing the projecting end55of the projecting rib52toward the edge side in the Y-axis direction, as in the comparative example140.

From the comparisons described above, the inventors have found that forming the outer recess35as in the comparative example140greatly contributes to a reduction in the stress of the anti-root of the distal end portion. In addition, the inventors have further found that the stress of the anti-root can be further improved by directing the projecting end55of the projecting rib52toward the distal end in the longitudinal direction of the piezoelectric cantilever13a, as in the comparative example140.

The inventors have further found that the stresses of the root19and the anti-root in the distal end portion of the piezoelectric cantilever13acan both be improved, as in the embodiment of the present invention (i.e. the light deflector1) in Table 1, by adding the inner recess37to the vertical side22a, as in the comparative example120.

The inventors have also studied whether the damage to the distal end portion can be restrained by increasing the width (the dimension in the X-axis direction) of the piezoelectric cantilever13a, in place of the outer recess35, the inner recess37and the projecting end55directed toward the edge side. As a comparative example for this purpose, the dimension in the X-axis direction of the distal end portion inFIG. 4Awas increased. Further, the distal end portions of this comparative example and the light deflector1were compared in terms of limit deflection angle of the reflector2about the second axis Ub.

The result indicated that the limit deflection angle of the light deflector of the comparative example in which the width of the piezoelectric cantilever13ahas been increased was 13.5 degrees, while the limit deflection angle of the light deflector1was 18 degrees. The comparative example is inferior in the limit deflection angle to the light deflector1and the increased width of the piezoelectric cantilever13adisadvantageously leads to an increase in the size of the light deflector.

The value of the limit deflection angle is indicated by the absolute value of a maximum deflection angle on a positive side or a negative side, a half value, i.e. the deflection angle obtained when the reflector2faces directly forward being defined as zero degrees. Therefore, in the light deflector1, the reflector2oscillates at a deflection angle of 36 degrees (=18 degrees×2) about the second axis Ub.

Modification Example

In the light deflector1according to the embodiment, the inner piezoelectric actuators4acting as the first piezoelectric actuators that oscillate the reflector2about the first axis Ua by twisting the torsion bars3, and the inner frame5that oscillates the reflector2about the X-axis by the outer piezoelectric actuators6acting as the second piezoelectric actuators are shaped like the track of an athletic stadium in a front view. However, the light deflector in accordance with the present invention can be formed in other shapes (e.g. circular or elliptical).

The light deflector1of the embodiment is provided with all the outer recess35, the inner recess37and the projecting end55directed toward the distal end. However, the effect for restraining the damage to the distal end portion and the effect for increasing the limit deflection angle can be enhanced in steps by adding the outer recess35, the projecting end55directed toward the distal end, and the inner recess37in this order.

In the light deflector1of the embodiment, the projecting end55of the projecting rib52reaches the vertical side22b. However, in the light deflector according to the present invention, the projecting end of the projecting rib may be slightly separated from the vertical side22btoward the vertical side22awhile keeping the projecting end in the corner portion36.

In the light deflector1of the embodiment, the encircling rib51is formed over the full width of the rear surface of the inner frame5. However, in the light deflector according to the present invention, the encircling rib may be formed only on one side of the width of the inner frame, omitting the encircling rib on the other side thereof.

In the light deflector1of the embodiment, the inner frame5is shaped like the track of an athletic stadium. However, in the light deflector according to the present invention, the inner frame may be formed in other circular shapes which are longer in the direction of the first axes thereof than in the direction of the second axes thereof, such as an elliptical shape, or further an annular shape.

It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.