Abstract:
The invention relates to a device for the reflection of optical beams ( 25 ), provided with a piezo-plate ( 14 ), which has piezo-electric regions ( 15, 16 ), controlled by piezo electrodes ( 20, 21 ). At least one end section ( 22 ) of the piezo plate ( 14 ) is free of piezo electrodes ( 20, 21 ), whereby said free end section ( 22 ) is of a size, corresponding to the dimensions of the beams falling thereon. A deflection is thus achieved which leaves the wavefronts of the beams ( 25 ) essentially undisturbed.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a device for deflecting optical beams, comprising a piezo plate having piezoelectric regions and comprising piezo electrodes, disposed on surfaces, to drive said piezo plate. 
     A device of this kind is known from the article “Piezoelectric bimorph optical beam scanners: analysis and construction,” by J. Kelly Lee, published in Applied Optics, Vol. 18. No. 4, pp. 454-459. In this prior device, a mirror is mounted on a piezo plate. When the device is driven by piezo electrodes with a control voltage in the medium voltage range, the mirror moves as a result of the flexure induced in the piezo plate. A disadvantage of this device is the comparatively high mass that must be moved, which is an obstacle to rapid drive. 
     The object of the invention is to provide a device of the first-cited type that is distinguished by rapid drivability and distortion-free deflection. 
     SUMMARY OF THE INVENTION 
     This object is achieved according to the invention in a device of the first-cited type by the fact that the piezo plate is free of piezo electrodes in at least an end portion. 
     Because there are no piezo electrodes in an end portion of the piezo plate, no flexure is induced in that end portion, which instead remains substantially planar. If the electrode-free end portion is dimensioned to be relatively large compared to the dimensions of the beams incident thereon, reflection or transmission by the end portion will result in little or no distortion of the wave fronts and thus of the beam characteristic, especially the divergence. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a piezo plate having two piezo layers in which the spontaneous polarization has the same orientation; 
     FIG. 2 is a perspective view of a second exemplary embodiment of the invention, comprising a piezo plate having two piezo layers in which the spontaneous polarization is of opposite orientation; 
     FIG. 3 is a side view of the embodiment of FIG. 2 during the deflection of a light beam; 
     FIG. 4 is a perspective view of a third exemplary embodiment of the invention, comprising capacitive electrodes; 
     FIG. 5 is a perspective view of a fourth exemplary embodiment of the invention, comprising an internal beam guiding arrangement; 
     FIG. 6 is a side view of a fifth exemplary embodiment of the invention, comprising a piezo plate having two arms for mounting purposes; 
     FIG. 7 is a plan view of the embodiment of FIG. 6; 
     FIG. 8 is a perspective view of a sixth exemplary embodiment for two-dimensional deflection; and 
     FIG. 9 is a side view of a seventh exemplary embodiment of the invention, comprising regions of alternating orientation. 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a perspective view of a first exemplary embodiment of the invention. The exemplary embodiment of FIG. 1 comprises a flat piezo plate  1  that has a rectangular base surface and contains two individual piezo layers  2 ,  3  in which the spontaneous polarization has the same orientation, perpendicular to the plane of said piezo layers  2 ,  3 . At a first narrow end side, piezo plate  1  is clamped into a mounting unit  4  by means of two mounting bars  5 ,  6 . 
     Each piezo layer  2 ,  3  is provided on its outward-facing large side with an outer electrode  7 ,  8  as a piezo electrode. A middle electrode  9  is also provided as a piezo electrode between piezo layers  2 ,  3 . Each outer electrode  7 ,  8  and middle electrode  9  extend from the first narrow end side toward the opposite, second narrow end side, an end portion  10  of the second narrow end side being free of outer electrodes  7 ,  8  and middle electrode  9 . 
     Each outer electrode  7 ,  8  is connected electrically to an assigned outer-electrode contact  11 ,  12 , while middle electrode  9  is connected electrically to a middle-electrode contact  13 . The application of a voltage in the medium voltage range between middle-electrode contact  13  and each outer-electrode contact  11 ,  12 , using voltages of opposite polarity, drives piezo plate  1  to flex longitudinally about the transverse axis in the region of outer electrodes  7 ,  8  and middle electrode  9 . 
     FIG. 2 is a perspective view of a second exemplary embodiment of the invention. In the following explanation, data subscripted “ 1 ” refer to the crystal coordinate system and data subscripted “ 2 ” refer to the coordinate system of the piezo plate. The exemplary embodiment of FIG. 2 includes a flat, crystalline, Y 2 -cut piezo plate  14  having a rectangular base surface and comprising two piezo layers  15 ,  16 , the spontaneous polarization in the plane of piezo layers  15 ,  16  being oriented in opposite directions. Piezo layers  15 ,  16  are, for example, fabricated by heating to effect local domain inversion. Z 2  axes of the cartesian coordinate system of the piezo crystal are oriented parallel to the long side of the piezo plate  14 , while the Y 2  axis of the piezo plate  14  is rotated with respect to the Y 1  crystal axis by an angle of typically about 120° to 160°, with the coincident X 1  and X 2  axes as the axis of rotation. As in the first exemplary embodiment, described with reference to FIG. 1, the piezo plate  14  is clamped by a first narrow end side into a mounting unit  17  by means of two mounting bars  18 ,  19 . 
     Each piezo layer  15 ,  16  of piezo plate  14  according to the second exemplary embodiment is occupied on its outward-facing large side by an outer electrode  20 ,  21  as a piezo electrode. Each outer electrode  20 ,  21  extends from the first narrow end side toward the opposite, second narrow end side, an end portion  22  of the second narrow end side remaining free of outer electrodes  20 ,  21 . 
     Each outer electrode  20 ,  21  is connected electrically to an assigned outer-electrode contact  23 ′,  24 . The application of a voltage in the medium voltage range between outer-electrode contacts  23 ,  24  drives piezo plate  14  to flex longitudinally about the transverse axis in the region of outer electrodes  20 ,  21 . 
     FIG. 3 is a side view of the second exemplary-embodiment according to FIG. 2 during the deflection of a light beam  25  incident, with a planar wavefront, for example, on end portion  22  free of outer electrodes  20 ,  21 . When a voltage is applied between outer-electrode contacts  23 ,  24 , piezo plate  14  flexes only in the region of outer electrodes  20 ,  21 , while end portion  22  struck by light beam  25  remains planar except in a comparatively narrow region of transition to the outer electrodes  20 ,  21 . This results in a reflection behavior similar to that of a plane mirror, and the reflected wavefront is not deformed with respect to the incident wavefront. 
     Similar flexural behavior is demonstrated by the piezo plate  1  of the first exemplary embodiment, depicted in FIG.  1 . 
     FIG. 4 is a perspective view of a third exemplary embodiment of the invention, which is presented as an improvement of the second exemplary embodiment described with reference to FIGS. 2 and 3. It is understood that the improving features can also be provided in connection with the first exemplary embodiment, described with reference to FIG.  1 . In the third exemplary embodiment, depicted in FIG. 4, a plate-like first counterelectrode  26 , an elongated second electrode  27 , and an elongated supplementary electrode  28  are provided. First counterelectrode  26  is arranged to confront an outer electrode  20 ,  21 . Supplementary electrode  28  is disposed on an outer face of a piezo layer  15 ,  16 , for example roughly in the center of end portion  22 , and extends transversely with respect to piezo plate  14 . Second counterelectrode  27  confronts supplementary electrode  28 . The mutually confronting outer electrodes  20 ,  21  and first counterelectrode  26  and the mutually confronting supplementary electrode  28  and second counterelectrode  27  form capacitively functioning electrodes. 
     Counterelectrodes  26 ,  27  are connected electrically to a first counterelectrode contact  29  and a second counterelectrode contact  30 , respectively. Supplementary electrode  28  is connected electrically to a supplementary-electrode contact  31 , while, in addition, outer electrode  21  confronting first counterelectrode  26  is connected to an outer-electrode supplementary contact  32 . 
     The application of a voltage, typically in the medium voltage range, to first counterelectrode contact  29  and outer-electrode supplementary contact  32  and to second counterelectrode contact  30  and supplementary-electrode contact  31  causes forces to be exerted on piezo plate  14 , as a function of the polarity of the applied voltage, between the associated outer electrode  2 l and first counterelectrode  26  and between supplementary electrode  28  and second counterelectrode  27 ; these forces are superimposed on the piezoelectrically exerted forces and, especially if the polarity is appropriate, amplify the deflection. 
     In modifications of the third exemplary embodiment described with reference to FIG. 4, only one pair is provided out of confronting outer electrodes  21  and first counterelectrode  26  and confronting supplementary electrode  28  and second counterelectrode  27 . 
     FIG. 5 is a perspective view of a fourth exemplary embodiment of the invention, which includes some of the features of the third exemplary embodiment described with reference to FIG. 4; these features have been given the same reference numerals and will not be described in more detail below. The fourth exemplary embodiment of FIG. 5 includes highly reflective outer electrodes  20 ,  21 . A decoupling antireflection coating  33  has been deposited in end portion  22  free of outer electrodes  20 ,  21 . In addition, the piezo plate  14  projects by an incoupling portion  34  beyond mounting unit  17 . Incoupling portion  34  is provided with an incoupling antireflection coating  35  and a reflection coating  36 , by means of which a light beam  25  can be coupled into piezo plate  14 . After multiple reflections on outer electrodes  20 ,  21 , light beam  25  exits piezo plate  14  without deformation through decoupling antireflection coating  33  in end portion  22  free of outer electrodes  20 ,  21 . The exit direction depends on the electrical drive and the associated flexure of the piezo plate  14  longitudinally about the transverse axis. 
     FIGS. 6 and 7 are a lateral and a plan view, respectively, of a fifth exemplary embodiment of the invention, comprising a piezo plate  37  that has the same piezoelectric structure as piezo plate  14  described with reference to FIG. 2, taking the form of two piezo layers  38 ,  39  with the spontaneous polarization in the plane of said piezo layers  38 ,  39  oriented in opposite directions. Piezo plate  37  is realized with two outwardly projecting arms  40 ,  41  in its middle region. The arms  40 ,  41  are engaged with a tilt mounting  42  by means of which piezo plate  37  is swivelably mounted. 
     As in the previously described exemplary embodiments, disposed on the one side of piezo plate  37  as piezo electrodes are outer electrodes  43 ,  44 , which extend from tilt mounting  42  into an end region  45  free of outer electrodes  43 ,  44 , to permit the reflection of a beam  46  without deformation and with the ability to control the direction of reflection. 
     Arranged to confront each other in the end portion on the other side of piezo plate  37  are a supplementary electrode  47  and a counterelectrode  48 , to which, as capacitively functioning electrodes, an electrical voltage in the medium voltage range can be applied. 
     The driving of outer electrodes  43 ,  44 , supplementary electrode  47  and counterelectrode  48 , causes piezo plate  37  to flex longitudinally about the transverse axis and to tilt about arms  40 ,  41 . 
     FIG. 8 is a perspective view of a sixth exemplary embodiment for two-dimensional deflection of a beam, comprising a flat, crystalline piezo plate  49  with a rotated Y 2  cut and a rectangular base surface, comprising two piezo layers  50 ,  51 . The Z 2  axis of the Cartesian coordinate system of the piezo crystal is oriented at an angle of approximately 40° to approximately 60° with respect to the long side of piezo plate  49 , The spontaneous polarizations of piezo layers  50 ,  51  are of opposite directions in the piezo plate  49  of the sixth exemplary embodiment, and are produced, for example, by heating to effect local domain inversion. The piezo plate  49  is clamped by a first narrow end side in a mounting unit  52  comprising two mounting bars  53 ,  54 . 
     Each piezo layer  50 ,  51  of the piezo plate  49  according to the sixth exemplary embodiment is occupied on its outward-facing large side by an outer electrode  55 ,  56  as a piezo electrode. Each outer electrode  55 ,  56  extends from the first narrow end side toward the opposite, second narrow end side, an end portion  57  of the second narrow end side remaining free of outer electrodes  55 ,  56 . 
     Each outer electrode  55 ,  56  is connected electrically to an assigned outer-electrode contact  58 ,  59 . The application of a voltage in the high-voltage range between outer-electrode contacts  58 ,  59  drives piezo plate  49  to twist about the longitudinal axis in the transverse direction in the region of outer electrodes  55 ,  56 , so that the end portion  57  can be tilted parallel to mounting unit  52  and a beam incident on end portion  57  can be deflected in a given direction. 
     In addition, mounted on a large side of end portion  57  is a supplementary electrode  60 , which with a counterelectrode  61  spacedly confronting it forms a capacitively functioning electrode pair. Supplementary electrode  60  is connected electrically to supplementary-electrode contact  62 , while counterelectrode  61  is connected to a counterelectrode contact  63 . When supplementary electrode  60  and counterelectrode  61  are driven by means of a voltage in the low-voltage range, piezo plate  49  is flexed longitudinally about the transverse axis. When the flexure that can be generated by supplementary electrode  60  and counterelectrode  61  is superimposed on the tilt that can be induced by means of outer electrodes  55 ,  56 , the result is two-dimensional deflection of a beam incident on end portion  57 . 
     In an exemplary embodiment not shown, to achieve two-dimensional deflection, two devices according to the invention, for example according to one of the exemplary embodiments of FIGS. 1 to  7 , are arranged with respect to each other so that the directions of flexure can be oriented perpendicular to each other. 
     FIG. 9 is a side view of a seventh exemplary embodiment of the invention. The seventh exemplary embodiment depicted in FIG. 9 comprises a piezo plate  65  fabricated from a Z 1 -cut crystal. The piezo plate  65  is realized with a number of strip-like first domains  66  and second domains  67  extending over the entire thickness as regions of orientation, the orientation of the piezoelectrically operative axes being the same in each case. In the piezo plate  65 , the Y 1  axes of the domains  66 ,  67  are oriented parallel to the long side, whereas by domain inversion the Z 1  axes of the first domains  66  have been oriented oppositely to the Z 1  axes of the second domains  67 . The Y 1  axes of domains  66 ,  67  are therefore also oriented oppositely to each other. The piezo plate  65  is clamped at a first narrow end side in a mounting unit  68  comprising two mounting bars  69 ,  70 . 
     Provided as piezo electrodes along the edge regions of a number of domains  66 ,  67 , on both large sides of piezo plate  65 , are strip-like strip electrodes  71 ,  72  that are narrow in comparison to the width of the domains  66 ,  67 , with an end portion  73  remaining free of strip electrodes  71 ,  72 . Voltages of alternating polarity in the medium-voltage range can be applied to a large side of each of the adjacently arranged strip electrodes  71 ,  72 , and mutually confronting strip electrodes  71 ,  72  on different large sides can also be subjected to voltages of alternating polarity. This causes piezo plate  65  to flex longitudinally about the transverse axis in the region of strip electrodes  71 ,  72  according to the magnitude of the applied voltages, while the end portion  73  free of strip electrodes  71 ,  72  remains substantially planar. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.