Abstract:
A wideband optical beam deflector utilizes an electromechanical transducer to simultaneously rotate a plurality of mirrors. An incoming optical beam is successively reflected by these rotating mirrors such that the deflections of the mirrors are additive. the deflector may also incorporate a stationary mirror to complete the reflector path

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to an optical beam deflection apparatus and in particular to a wideband optical beam deflection apparatus which utilizes a high frequency electromechanical transducer to actuate a plurality of mirrors to deflect an incoming optical beam. 
     2. Disclosure Statement 
     This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior-art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends upon uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of materials which might lead to a discovery of pertinent material, though being not of themselves pertinent. 
     Devices for deflecting an optical beam are useful in oscillography, in the recording and retrieval of information from an optical store and as the actuating means in an optical servo loop. Mirror galvanometers, which are commonly used in these applications, utilize a mirror mechanically coupled to a coil which moves with a magnetic field (known as a d&#39; Arsonval mirror galvanometer). Those mirror galvanometers with the smallest mirrors may have a useful frequency response up to several thousand hertz, but the frequency response drops sharply as the mass of the mirror increases. The use of small mirrors, however, limits the aperture of the optical beam that may be used with them. 
     Where higher frequency response is required, acousto-optical deflectors have been used. Acousto-optical deflectors have a frequency response up to one megahertz, however, these devices are comparatively expensive. Furthermore, acousto-optical deflectors require signal processing electronics and well-collimated monochromatic radiation, as well as requiring careful angular adjustment with respect to the optical beam to be deflected. 
     Various optical beam deflection devices are disclosed in the prior art. For example, U.S. Pat. No. 3,902,783 discloses a beam deflector having a pair of piezoelectric transducers which have opposite states of expansion and contraction, the transducers both being connected to a rocker which rotates a pair of mirrors. 
     U.S. Pat. No. 3,753,199 discloses a beam deflector having a pair of piezoelectric transducers rigidly cantilevered at one end from a support member and articulately connected at the other end to a mirror. 
     U.S. Pat. No. 3,612,642 discloses an optical scanner having first and second mirrors mounted on the tines of an electronically driven torsional tuning fork, the mirrors being oscillated thereby. An incoming beam of light is directed toward the first mirror which reflects it onto the second mirror, the second mirror directing the beam onto a fixed third mirror. The third mirror acts to duplex the beam by directing it back ot the second mirror, which returns its beam to the first mirror. 
     SUMMARY OF THE INVENTION 
     This invention is directed toward an apparatus for deflecting an optical beam. In general, this is accomplished by utilizing a high frequency electromechanical actuator such as one of the piezoelectric type, to drive a plurality of moving mirrors. One side of each of the moving mirrors is attached to a rigid frame through a hinge. A linkage couples the opposite side of each of these mirrors to the actuator. An alternative embodiment utilizes a fixed mirror, to provide a reflection path whereby the optical beam is directed toward an adjacent mirror. 
     Other alternative embodiments utilize a fixed mirror to reflect the beam back upon the moving mirrors such that the output beam leaves the plane of the incident optical beam by a few degrees. 
     Many additional features and advantages of the invention will be apparent from a reading of the specification in which illustrative embodiments of the invention are described in detail. This specification is to be taken with the accompanying drawing in which the various characteristics of the preferred embodiments are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a top plan view of an apparatus embodying the present invention. 
     FIG. 2 is a top plan view of the apparatus of FIG. 1, illustrating the deflection of an optical beam in response to movement of the output arm. 
     FIG. 3 is a top plan view of a second alternative embodiment of the present invention. 
     FIG. 4 is a top plan view of a third alternative embodiment of the present invention. 
     FIG. 5 is a top plan view of a fourth alternative embodiment of the present invention. 
     FIG. 6 is a top plan view of the apparatus of FIG. 5, illustrating the deflection of an optical beam in response to the movement of the output arm. 
     FIG. 7 is a top plan view of a fifth alternative embodiment of the present invention. 
     FIG. 8 is a side sectional view of the apparatus of FIG. 2 taken along line 8--8. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawing wherein identical reference numerals refer to similar elements, FIG. 1 shows a wideband optical beam deflector at 10. The deflector 10 utilizes a set of moving mirrors 12, 14, 16 and 18. The moving mirrors 12, 14, 16 and 18 are attached to a frame 20 by a set of hinges 22, 24, 26 and 28 respectively. The hinges 22, 24, 26 and 28 may be flexure strips, torsion rods or other types of hinges which are well known in the art. A linkage 30 is coupled to a single electromechanical actuator 32 through an output arm 34. A pivot point 36 couples the moving mirrors 14 and 16 to the linkage 34, while a pivot point 38 couples the moving mirrors 12 and 18 to the linkage 30. As shown in FIG. 8, the linkage 30 has an aperture 40 for the passage of incoming and outgoing optical beams. The frame 20 also has an aperture 42 for the passage of incoming and outgoing optical beams. In order to provide structural rigidity to the frame 20, the aperture 42 may be of non-reflecting glass. The aperture 42 may also be merely an opening in the frame 20. A stationary mirror 44 is attached to the frame 20 adjacent to the mirrors 16 and 18. 
     In operation, an optical beam 46 enters through the aperture 42. The optical beam 46 is successively reflected by the mirrors 14, 18, 44, 16 and 12 and exits through the aperture 42. An electrical signal which is applied to the actuator 32 caused the output arm 34 to move back and forth. The actuator 32 may be a piezoelectric, magnetostrictive or any other electromechanical transducer which has the desired frequency response and which produces motion in the required directions. 
     As the output arm 34 moves back and forth, the linkage 30 causes the mirrors 12, 14, 16 and 18 to rotate through a small angle about their substantially parallel axes. As shown in FIGS. 2 and 8 when the linkage 30 moves away from the actuator 32 the mirrors 12 and 14 rotate clockwise and the mirrors 16 and 18 rotate counterclockwise. The effect on the optical beam 46 is therefore additive resulting in a deflection of the optical beam 46 in a clockwise direction. By utilizing a plurality of mirrors in the arrangement shown in FIG. 1, the amount of deflection is substantially greater than that of a single mirror. 
     FIG. 3 shows a second embodiment wherein a second stationary mirror 48 has been added to the apparatus of FIG. 1. In operation, the optical beam 46 enters through the aperture 42 and is successively reflected by the mirrors 14, 18, 44, 16, 12, 48, 12, 16, 44, 18 and 14 in that order. In the embodiment shown in FIG. 3, the outgoing optical beam 46 may be separated from the ingoing optical beam 46 by orienting the mirror 48 such that the outgoing optical beam 44 is in a slightly different plane than that of the ingoing optical beam 44. The use of the mirror 48 results in approximately twice the deflection per unit input signal as with the embodiment shown in FIG. 1. 
     The frequency response of the deflector 10 may be increased by lowering the mass of the mirrors 12, 14, 16 and 18 as shown in FIG. 4. In FIG. 4, mirrors 13, 15, 17 and 19 are shaped to reduce their mass. By structuring each mirror such that it is thicker at its center and tapered at its ends, undue flexure which may contribute to distortion of the optical wavefront, undesired resonances or non-linearity of response is minimized. In order to further eliminate undesirable flexural modes of the mirrors, the center portion of the rear of each mirror may be ribbed. 
     FIG. 5 shows an embodiment wherein the mass of the moving mirrors is reduced by removing the mirrors 12 and 16 of the FIG. 1. In addition, the hinges 22 and 26 of FIG. 1 may be omitted. In operation, as the beam 46 enters through the aperture 42, the beam 46 is successively reflected off the mirrors 14 and 18 and exits through an aperture 50. Since only two moving mirrors are utilized in this embodiment, the amount of deflection per unit electrical signal is less than with the embodiments shown in FIGS. 1, 2, 3 and 4. As shown in FIG. 6, when the linkage 30 moves away from the actuator 32, the mirror 14 rotates clockwise and the mirror 18 rotates counterclockwise. The effect on the optical beam 46 is therefore additive resulting in a greater deflection of the optical beam 46 than would be possible with a single mirror. 
     FIG. 7 shows an embodiment where the amount of deflection per unit electrical signal is increased by replacing the aperture 50 with a stationary mirror 52. In operation, the optical beam 46 is reflected off the mirrors 14, 18, 52, 18 and 14 in that order. The outgoing optical beam 46 may be separated from the ingoing optical beam 46 by orienting the mirror 52 such that the outgoing optical beam 46 is in a slightly different plane than that of the ingoing optical beam 46. 
     It is to be understood that the subject invention has been described by reference to specific embodiments and that many additions and modifications thereto will be apparent to those skilled in the art. Accordingly, the foregoing description is not to be construed in a limiting sense.