Abstract:
The flexible prism is comprised of two thin, rigid, optically transparent plates sandwiching an optically transparent deformable material such as a transparent liquid or a transparent flexible solid. The index of refraction for all of the materials is preferably matched, such that reflections between interfaces are minimized. The liquid/flexible material used in this flexible prism may consist of almost any substantially transparent material that is not rigid like a solid glass. The angles of one or both of the rigid surfaces of the flexible prism can be selectively adjusted with a respect to a spectrally narrow beam of light passing through the prism so as to produce the refraction desired.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/386,101, filed on Jun. 5, 2002, which provisional application is incorporated by reference herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    Our invention relates generally to the optical steering of a spectrally narrow beam of light.  
         BACKGROUND OF THE INVENTION  
         [0003]    A several methods exist for steering of a beam of collimated light. One method is to simply adjust the pitch and yaw (X and Y-axis) of the entire light source to aim the beam in a new direction. However, this is not always desirable if the light source is mechanically constrained, the cost of mechanical adjustment is expensive, or the speed of mechanically adjusting the entire light source is too slow for the intend application.  
           [0004]    A very common arrangement is to use a mirror to fold the collimated beam in a new direction. This has had great success in devices ranging from astronomical telescopes to Digital Mircromirror Devices. This method is not ideal in all cases. The one mirror can no longer steer the beam as if it was a transmissive optical element. To have the redirected beam propagate in the direction of the original beam, more than one mirror is required, which decreases the linearity of the optical system.  
           [0005]    One technique to maintain the linearity of an optical system is to use a transmissive lens or a series of lenses that collimate a beam of light. The lens can then transmit the beam on forward in a collimated fashion. If one wants to redirect the beam slightly, either the lens or the original light source must de-center a small amount. This introduces aberrations in the light beam thereby decreasing its optical quality. Secondly, it decreases the linearity of the system a small amount, as it now requires some mechanism of adjustment from the side, which decreases the compactness of a linear system.  
           [0006]    A method of maintaining a high optical quality collimated light beam that is linear in fashion is to use a series of two optical prisms. The two in-series prisms have the ability to steer a spectrally narrow optical light beam by rotating the two prisms around their individual center or optical axis and does not increase the non-linearity of the optical system. However, they may be slow to adjust whether electrically controlled or mechanically controlled and the added expenses of the prisms themselves may not be justified for some optical systems.  
           [0007]    Lastly, Electro-optical systems use a nonlinear optical feature that is not present in the other methods, but do maintain a single on-axis optical system. The steering speed is relatively fast, but these Electro-optical systems are very expensive and have some attenuation of the light beam.  
           [0008]    Nonetheless, despite the existence of the above-referenced systems, there exists the need for transmissive on-axis optical systems for directing a spectrally narrow beam of light that are: low cost when mechanically adjusted to steer the light beam; have the potential of high steering speed when electrically controlled; and will remain relatively low cost (compared to other methods of steering an optical light beam) when electrically controlled.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0009]    Our invention has the ability to transmit and steer a spectrally narrow light beam without introducing significant aberrations into the beam using an optical system that is all on one optical axis and is relatively low in cost. It is based on the use of a flexible prism. In the preferred embodiment of our invention, this flexible prism is comprised of two thin rigid plates. These plates, which are preferably formed from glass, are substantially transparent to the frequency of the spectrally narrow light beam. However, they need not be flat--one or both surfaces of either plate can be curved (and in this way produce, e.g., a collimating lens). Sandwiched between these plates is a deformable material that is substantially transparent to the frequency of the spectrally narrow light beam. However, The deformable material may take the form of a substantially transparent liquid or a substantially transparent flexible solid. The index of refraction for all of the materials are preferably matched, such that reflections between interfaces are minimized. However, even though it presents additional problems, our invention can function when the indexes of refraction of the various parts making up the flexible prism are different. The liquid/flexible material used in our flexible prism may consist of silicone, baby oil, uncured UV adhesive, or other material that is not rigid like a solid glass.  
           [0010]    In the preferred embodiments, where indexes of refraction are identical, the flexible prism can be treated as having only the two surfaces of a normal solid prism. Thus, when a laser (or other light source that is made to be spectrally narrow via a filter or other device) illuminates the flexible prism, it is directed in the same manner it would be directed by a normal solid prism. To begin with, it enters the flexible prism where the first flat surface it encounters is a rigid material that may or may not be coated to reduce back reflections. If the first surface is normal then the light will not refract and will pass directly onto the final flat surface, since the inside of the prism is index matched to the rest of the materials. At this final surface, refraction will take place and the beam will be deflected from the optical axis by an amount correlating to the angle of the final surface with respect to the optical axis.  
           [0011]    The surfaces of the flexible prism can be mechanically adjusted to produce the refraction desired. This mechanical adjustment of the prism surfaces can be accomplished by means of adjustment of other components via screws, piezoelectric transducers, and/or through magnetic or capacitive changes on the mounts of the flexible prism. In addition, both surfaces of the prism may be adjusted to ease the electrical or mechanical constraints on the optical system.  
           [0012]    Our flexible prism can also be used to switch a light beam on or off. If the light beam is headed towards the final surface, and this surface is at a critical angle or greater, then the light will not refract out of the system. The light beam will instead have close to one hundred percent reflection back into the prism. This is beneficial if the user needs to have zero percent transmission in the optical system. Thus, our flexible prism system can control the transmission properties of the optical system in an on/off manner. In effect, this serves to digitalize the system.  
           [0013]    Further, if the device is equipped with a fast means for accomplishing mechanical adjustments, such as electrical means, then our optical system can act as a scanner in two dimensions. In the act of scanning, it can also act as an optical switch: It is “on” when the prism surfaces are set to specific angles such that the light beam is deflected to another optical system or to a detector. The surface angles of the optical prism can then be adjusted relative to the optical axis such that the light is deflected to another optical system, a detector, or nothing at all. (The last alternative represents an “off” state like that made possible by a Digital Micromirror Device).  
           [0014]    The foregoing uses and benefits are, however, by no means exhaustive in nature. As should be obvious from the foregoing, the flexible prism of our invention is relatively simple in construction and operation. Moreover, it can be inexpensively produced and used. However, it is extremely versatile and can be used in innumerable ways to aim, adjust, digitalize, switch, or otherwise control a spectrally narrow beam of light. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1 provides a schematic perspective view of a flexible prism in accordance with the teachings of this invention.  
         [0016]    [0016]FIG. 2 provides a schematic perspective view of the flexible prism shown in FIG. 1 while it is subject to a force causing the final surface to be angled relative to the first surface.  
         [0017]    [0017]FIG. 3 provides a schematic side view of a mounted flexible prism showing the path of an unrefracted light beam through the prism.  
         [0018]    [0018]FIG. 4 provides a schematic side view of the mounted flexible prism illustrated in FIG. 3 while it is subject to a force causing the final surface to be angled relative to the first surface and the path of the light beam through the prism to be refracted.  
         [0019]    [0019]FIG. 5 provides a schematic side view of a mounted flexible prism having a flexible substance surrounding the flexible transparent material at its center.  
         [0020]    [0020]FIG. 6A provides a schematic side view of a mounted flexible prism showing adjustment screws for use in causing the final surface to be angled relative to the first surface of the flexible prism.  
         [0021]    [0021]FIG. 6B provides a schematic frontal view of the mounted flexible prism illustrated in FIG. 6A showing its four adjustment screws.  
         [0022]    [0022]FIG. 7 provides a schematic cross-sectional view of a laser sight utilizing a flexible prism for adjustment purposes.  
         [0023]    [0023]FIG. 8 provides a schematic perspective view of a smaller flexible prism.  
         [0024]    [0024]FIG. 9 provides a schematic perspective view, of an array of smaller flexible prisms.  
         [0025]    [0025]FIG. 10 provides a schematic side view of two pairs of prisms where light is directed to the out of line member.  
         [0026]    [0026]FIG. 11 provides a schematic side view of two pairs of prisms where light is directed to the in line member.  
         [0027]    [0027]FIG. 12 provides a schematic side view of a flexible prism at the critical angle that directs a light beam to suffer total internal reflection.  
     
    
     DETAILED DESCRIPTION  
       [0028]    Our invention is used in conjunction with an optical system to create a mechanism for redirecting or steering a spectrally narrow collimated beam of light. A light beam is sent into a flexible prism  16  whereby the beam is refracted, following Snell&#39;s law of refraction, and propagates to the final surface of the flexible prism  16  where the light beam is refracted again. The amount refraction is a function of the wavelength of the light beam and also the relative angles between the first surface and the final surface.  
         [0029]    A basic embodiment of our flexible prism invention  16  is shown in FIGS. 1 and 2. These figures show a front and back solid plate  10 ,  14  made out of glass, plastic, or some other rigid, optically transparent material. The flexible substance  12  located at its center between plates  10 ,  14  will typically consists of silicone, baby oil, epoxy, solgel, uncured/cured UV adhesive, or some other material that is not rigid like a solid glass. (Preferably, it will be index matched to the substance(s) forming the plates  10 ,  14 .) This allows the plates to be angled relative to each other as shown in FIG. 2.  
         [0030]    As illustrated in FIGS. 3, 4,  5 , and  6 , our flexible prism  16  will typically be mounted at the end of an optical system  20  to steer a light beam  22 ,  24 . In this case, the flexible prism  16  is mounted to the optical system in any fashion that allows transmission of the incoming optical light beam. For example, in FIGS. 3, 4,  5 , and  6 , the invention&#39;s back plate  10  is bonded with an adhesive to optical system  20 . FIG. 3 illustrates a light beam  22  passing through flexible prism  16  when it is under no force such that plates  10  and  14  are parallel to one another. In this circumstance, the direction of light beam  22  remains unchanged. However, when one of the plates is angled in some fashion relative to the other plate, light beam  24  is refracted in accordance with Snell&#39;s Law, changing the direction of light beam  24 . (See e.g., FIG. 4).  
         [0031]    If the force that caused one of the plates, either  10  or  14 , to be angled relative to the other is released, then the flexible substance  12 , if resilient, can act like a spring to force the plates  10 ,  14  back to their original parallel position. However, this is dependent on the nature of the flexible substance used. Some of the substances envisioned for use in our invention, such as baby oils, will not have this characteristic. In this case, a material  26  that is resilient can be placed around substance  12  and can also be used to provide resiliency. (See, FIG. 5). Resilient material  26  can also serve to maintain a liquid media used for flexible substance  12  in position. Alternatively, where one or both angled plates are to be fixed, an adhesive may be used for material  26  and used to fill up the gaps between plates  10  and  14  and substance  12 . Material  26  and/or flexible substance  12  can be cured in place if they are curable adhesives. This allows the flexible prism  16  to maintain its shape even after an original force imposed on it is released.  
         [0032]    A force causing one or both of the plates  10 ,  14  to be angled can be provided by various deformation systems. One example can be seen in FIGS. 6A, 6B, and  7 . FIG. 6A provides a side view of a flexible prism  16  mounted on the front of an optical system  20  with adjustment screws  32  in its housing  30  serving as actuators for its deformation system. The front view of this arrangement is shown in FIG. 6A. In this system, screws  32  are adjusted to apply force on plate  14  such that plate  14  is angled relative to plate  10 . This configuration allows the user to then steer the beam to a new direction simply by adjusting screws  32 .  
         [0033]    The type of robust deformation system illustrated in FIGS. 6A and 6B is suitable for numerous uses, including use in adjustment of laser alignment systems (also known as laser sighting systems) such as those used in surveying and with firearms. In the context of firearms, the system illustrated in FIGS. 6A and 6B could be considered as part of a laser module positioned on a firearm, in a firearm&#39;s barrel, or in the recoil spring guide for an automatic pistol as described in U.S. Pat. Nos. 4,934,086 and 5,509,226. In these applications, the illustration shown in FIG. 6A would constitute a view of the laser beam emitting end of a laser module. A more specific example of the use of our invention in a laser sight is seen in FIG. 7, which illustrates a laser sight having a body  100  coupled to a head  101 . A laser diode  102  is positioned in body  100  so as to project a laser beam forward through a collimating lens  103  in head  101 . From there it would travel through the flexible prism assembly (indicated generally by bracket  104 ). Flexible prism assembly  104  includes plates  10 ,  14  sandwiching flexible substance  12 , as in past embodiments illustrated. It is adjusted by exerting pressure on an intermediate rigid washer  105  by screws or otherwise as previously discussed. Washer  105  helps to insure that uneven pressure does not result in the breakage of plate  14 . It is assisted in this by the presence of a flexible O-ring  106  that serves as a shock absorbing and cushioning base for plate  10 .  
         [0034]    Our flexible prism  16  can also be miniaturized so as to become a small flexible prism  50  as shown in FIG. 8. The front and back plates  44 ,  40  can still be made out of any solid transparent material while substance  42  still transmits some portion of the desired wavelength(s). Actuators  46  for a deformation system are shown schematically. At these small scales, flexible substance  42  can be controlled to some degree electrically as with liquid crystal. If flexible prism  50  is small enough, the mechanical forces applied by actuators  46  could be provided via capacitive, electrostatic, thermal, acoustical and/or magnetic actuators. If the flexible prism  50  is small, yet too large for the previously mentioned forces, then small mechanical forces could be applied by actuators  46  via piezoelectric transducers to control one or both plates  40 ,  44 .  
         [0035]    Systems using small flexible prisms  16  such as those described are extremely useful in photonics, where they allow rapid switching, digitalization and precise control of optical systems. For example, a small flexible prism  50  could be mounted to an optical conductor such as an optical fiber that has had exiting light collimated with a lens. The small flexible prism  50  could then steer the light beam from the fiber to another optical conductor or fiber and act as an optical switch.  
         [0036]    Taking this idea further, FIG. 9 shows a two dimensional array  48  of these miniature flexible prisms  50  that could be made to steer a multitude of light beams. FIGS. 10 and 11 provide diagrammatic side views showing a smaller array of  4  miniature flexible prisms  50  steering two light beams with the capability to switch back and forth. In FIG. 10, miniature flexible prisms  60  direct light beam  68  to flexible prism  66 , which receives the light beam  68  and redirects the beam such that it is parallel to the original incoming beam  68  on prism  60 . Prism  62  directs light beam  69  to prism  64 , which receives the light beam  69  and redirects the beam such that it is parallel to the original incoming beam  69  on prism  62 . If no deformation system forces are applied, as shown in FIG. 11, beam  68  passes directly through prism  60  and on to prism  64 . Likewise, beam  69  passes directly through prism  62  and on to prism  66 .  
         [0037]    Finally, FIG. 12 illustrates a situation where a flexible prism  16  is deformed to such an extent that plate  14  is at the critical angle or greater relative to plate  10 . In this case light beam  72  will suffer total internal reflection off of the last surface where plate  14  meets the air interface. This does not allow any light to pass though flexible prism  16 .