Abstract:
Optical lenses, systems, devices and methods for fabricating and manufacturing diffractive waveplate lenses that allow setting the focal length sign of an optical system by positioning the lens with its front or back surface with respect to an incoming circular polarized light beam. Applications for the lenses include optical systems comprising fibers, diode lasers, waveplates, polarizers, and variable lenses, particularly, in the form of a set of polymer films with re-attachable adhesive layers. And providing a flat mirror with concave or convex function due to diffractive waveplate lens coating.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to U.S. Provisional Application Ser. 61/980,062 filed Apr. 16, 2014, the entire application of which is incorporated by reference in its&#39; entirety. 
     
    
     GOVERNMENT LICENSE RIGHTS 
       [0002]    This invention was made in part with U.S. Government support under Army Contract No. W911QY-12-C-0016. The government has certain rights in this invention. 
     
    
     FIELD OF INVENTION 
       [0003]    This invention relates to optical lenses, and in particular to systems, devices, and methods of fabricating and manufacturing optical lenses used for imaging optics and systems, astronomy, displays, polarizers, optical communication and other areas of laser and photonics technology. 
       BACKGROUND OF THE INVENTION 
       [0004]    The present invention is in the technical field of optics. More particularly, the present invention is in the technical field of lenses, systems of lenses, imaging and controlling of light beams. Lenses are commonly made by shaping an optical material such as glass. The weight of such lenses increases strongly with diameter making them expensive and prohibitively heavy for applications requiring large area. Also the quality of a lens typically decreases with increasing size. To achieve desirable features such as high-quality imaging, conventional lenses sometimes have curved surfaces that are non-spherical. The need to grind and polish conventional lenses with non-spherical surfaces can make such lenses extremely expensive. Segmented lenses such as Fresnel lenses are relatively thin, however, the structural discontinuities result in severe aberrations. Uses of holographic lenses are limited by the compromise of efficiency, spectral bandwidth and dispersion. Thus, there is a need for lenses that could be obtained in the form of thin film structurally continuous coatings on a variety of substrates for a variety of spectral ranges. 
         [0005]    Thus, the need exists for solutions to the above problems with the prior art. 
       SUMMARY OF THE INVENTION 
       [0006]    A primary objective of the present invention is to provide systems, devices, and methods for providing a structurally continuous thin film lens wherein the sign of its focal length can be chosen to be positive or negative by flipping the lens. 
         [0007]    The second objective of the present invention is providing an imaging system comprising a DW lens with spherically or cylindrically symmetric continuous structure, deposited on a variety of substrate such as optical fiber facet, a refractive lens, a birefringent lens, a phase retardation plate or a tunable lens. 
         [0008]    The third objective of the present invention is providing sunglasses, swimming goggles, and goggles for eye protection that employ continuous thin film structures, that correct for human vision defects as do conventional prescription sunglasses or goggles but that perform this function without requiring curved lens surfaces. 
         [0009]    The fourth objective of the present invention is providing a lens with continuous thin film structure whose properties can be changed in a useful way by application of an electrical potential to the lens. 
         [0010]    The fifth objective of the present invention is providing a lens with a continuous thin film structure on a non-planar surface. 
         [0011]    The sixth objective of the present invention is providing a flat mirror coated with a continuous thin film structure that focuses or defocuses light. 
         [0012]    Further objects and advantages of this invention will be apparent from the following detailed description of the presently preferred embodiments which are illustrated schematically in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  shows spatial distribution of optical axis orientation in spherical diffractive waveplate lenses of one sign. 
           [0014]      FIG. 1B  shows spatial distribution of optical axis orientation in spherical diffractive waveplate lenses of an opposite sign. 
           [0015]      FIG. 2A  shows a representation of a spherical diffractive waveplate lens with continuous alignment lines of anisotropy axis of the birefringent material. 
           [0016]      FIG. 2B  shows spherical diffractive waveplate lenses of opposite signs in description with continuous alignment lines. 
           [0017]      FIG. 3  shows a diffractive waveplate lense viewed from opposite sides. 
           [0018]      FIG. 4A  shows polarization properties of focusing and defocusing of a right-hand circular polarized beam by a diffractive waveplate lens, respectively. 
           [0019]      FIG. 4B  shows polarization properties of focusing and defocusing a left-hand circular polarized beam by a diffractive waveplate lens, respectively. 
           [0020]      FIG. 5A  shows the structure of a cylindrical diffractive waveplate lens. 
           [0021]      FIG. 5B  shows the structure of another cylindrical diffractive waveplate lens. 
           [0022]      FIG. 6A  shows the presence of both focused and defocused beams when an unpolarized light is incident on a diffractive waveplate lens. 
           [0023]      FIG. 6B  shows a method for spatially filtering out the defocused beam. 
           [0024]      FIG. 6C  shows the method for filtering out the defocused beam by a circular polarizer. 
           [0025]      FIG. 7  shows glasses having diffractive waveplate lens coatings. 
           [0026]      FIG. 8  shows a kit comprising diffractive waveplate lenses with reattachable adhesive backing. 
           [0027]      FIG. 9  shows application of a diffractive waveplate lens on a refractive lens. 
           [0028]      FIG. 10  shows a planar mirror converted into a focusing or defocusing mirror by addition of the diffractive waveplate lens coating. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its applications to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
         [0030]    In the Summary above and in the Detailed Description of Preferred Embodiments and in the accompanying drawings, reference is made to particular features (including method steps) of the invention. It is to be understood that the disclosure of the invention in this specification includes all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects and embodiments of the invention, and in the invention generally. 
         [0031]    In this section, some embodiments of the invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments. 
         [0032]    A list of components will now be described.
     101  left hand thin film     102  right hand thin film     201  continuous lines     301  observer     302  observer     400  component/element     410  right-hand circular polarized (RHCP) light beam     411  defocused RHCP light beam     412  focused RHCP light beam     420  left-hand circular polarized (LHCP) light beam     421  defocused (LHCP) light beam     422  focused LHCP beam     430  DWL layer     440  substrate     610  one-hand circular polarized light     612  focused light     620  opposite-hand circular polarized light     621  defocused light     630  DWL layer     640  substrate     650  aperture     660  circular polarizer     701  sunglasses     702  quarter wave phase retardation plate     703  DML film     801  DW lenses     802  functional layers     803  adhesive backing     804  support sheet     900  refractive lens     901  adhesive     902  DWL     1001  circular polarized collimated light beam     1002  DWL     1003  quarter waveplate     1004  flat mirror     1005  focused beam   
 
       GLOSSARY OF TERMS 
       [0070]    Diffractive waveplate (DWs): A birefringent film with anisotropy axis orientation modulated in the plane of the film. Different modulation patterns are possible resulting in different optical functionality, including lens, prism, axicon, etc. Generally, DWs may possess more than one layer, and the anisotropy axis may be modulated also in the bulk of the layer.
 
Diffractive waveplate lens: A diffractive waveplate with lens function. It may provide spherical, cylindrical, and other types of lens action.
 
Optical substrate or optical film: A transparent material providing mechanical support for DWs. It may be glass, quartz, plastic, or any other material that is at least partially transparent for the wavelengths of light that propagate through the DWs. It may possess anti-reflective or anti-scratch functions.
 
Switchable Diffractive waveplate: A DW that can be switched between diffractive and non-diffractive states upon application of external influences such as electric fields, temperature, optical radiation, etc. Generally, the switching can take place through gradual change of diffraction spectrum.
 
Variable phase retarder or polarization controller: An optical component capable of controlling the polarization of light propagated through it by applying electric fields, changing temperature, exposure to a light beam, etc. Particularly, it may be a liquid crystal sandwiched between substrates coated with transparent electrodes.
 
         [0071]    In the following description of the invention, the term “light” will often be used to describe the electromagnetic radiation that interacts with the diffractive waveplate lenses that are the subject of this invention. Although “light” generally means electromagnetic radiation with a wavelength in the visible region of the electromagnetic spectrum, it should be understood that the usage of the term “light” in the description is not restrictive, in the sense of limiting the design and application to diffractive waveplate lenses that operate only in the visible region of the spectrum. In general, all the designs and concepts described herein apply to operation over a wide range of the electromagnetic spectrum, including the microwave, infrared, visible, ultraviolet, and X-ray regions. While physical embodiments of diffractive waveplate lenses are at present advanced for operation in the visible region of the spectrum, the designs and applications disclosed here are applicable over all the noted regions of the electromagnetic spectrum. 
         [0072]    Many of the exemplary applications have been described herein with terms such as “light” being used to describe the electromagnetic radiation that is acted upon by the disclosed diffractive waveplate lenses. The term “light” in this context should not be taken to restrict the scope of the disclosed embodiments to only those in which the electromagnetic radiation acted upon or manipulated by the diffractive waveplate lenses is in the visible region of the spectrum. As will be evident to those skilled in the art, the exemplary embodiments disclosed here, in addition to being applicable in the visible region of the spectrum, are equally applicable to the microwave, infrared, ultraviolet, and X-ray regions of the spectrum. Exceptions to this generalization are the applications relating to human vision, for which operation in the visible region of the spectrum is required. 
         [0073]    The present invention relates to the design and application of diffractive waveplate lenses. The term “diffractive waveplate lens” as used herein describes a thin film of birefringent material deposited on a transparent structure, for example, a thin flat substrate of optical material such as glass. This birefringent film has the property that it retards the phase of light of one linear polarization by approximately one half wave (pi radians of optical phase) relative to the light of the other linear polarization. In diffractive waveplate lenses, the optical axis orientation depends on the transverse position on the waveplate, i.e. the position in the two coordinate axes perpendicular to the surface of the diffractive waveplate lens. In other words, the optical axis orientation is modulated in one or both of the transverse directions parallel to the surface of the substrate on which the active thin film is applied. Lensing action is due to parabolic profile of optical axis orientation modulation. 
         [0074]    There are two general types of diffractive waveplate lenses to which the present invention applies. The first type of diffractive waveplate lens is axially symmetric and is used, for example, to focus a collimated beam of light to a point in space. The second type of diffractive waveplate lens is cylindrically symmetric and is used, for example, to focus a collimated beam of light to a line segment in space. In many examples below, an optical system of circular symmetry is used as an example, but in general, all of the conclusions apply as well to optical systems of cylindrical symmetry. 
         [0000]    Lenses that Allow Choosing the Sign of the Focal Length Depending on Orientation 
         [0075]    In  FIG. 1 , the orientation of the anisotropy axis at each point of the birefringent thin film  101  is indicated by a short line segment. In the first type of diffractive waveplate lenses to which the present invention applies, illustrated in  FIG. 1A , the orientation of the anisotropy axis of the birefringent material including the thin film layer depends only on the radial distance r from a center point. This type of spherical diffractive waveplate lens is used for applications such as focusing a collimated beam of light to a point for imaging a distant scene onto a sensor array. To perform this function, the angle α that the anisotropy axis of the birefringent material makes with the coordinate axis is given by the following equation: 
         [0000]    
       
         
           
             α 
             = 
             
               
                 ± 
                 
                   
                     k 
                     0 
                   
                   
                     4 
                      
                     
                         
                     
                      
                     f 
                   
                 
               
                
               
                 r 
                 2 
               
             
           
         
       
     
         [0000]    where k 0 =2π/λ is the wavenumber of the light that is to be focused by the diffractive waveplate lens, λ is the wavelength of that radiation, f is the focal length of the diffractive waveplate lens (DWL), and r is the distance to the central point. 
         [0076]    The difference in signs in variation of the anisotropy axis with radius designate lenses of two opposite signs. The difference in corresponding patterns  101  and  102  in  FIGS. 1A and 1B  is even better visible in representation of the DWL structure by continuous lines  201  as shown in  FIG. 2A . DWLs of different signs correspond to the right- and left-spiraling patterns shown in  FIG. 2B , respectively. 
         [0077]    In the preferred embodiment of the present invention, DWLs of opposite optical axis modulation signs need not be two separate optical components and is obtained by rotating the DWL around an axis in the plane of the DWL by 180 degrees. The observers  301  and  302  looking at a given DWL from opposite sides as shown in  FIG. 3  see patterns of opposite sign. 
         [0078]    This optical asymmetry is described in detail in regard to  FIG. 4A  wherein the DWL layer  430  is shown on a substrate  440 . As an example, a right-hand circular polarized (RHCP) light beam  410  is transformed into a defocused left-hand circular polarized (LHCP) beam  421  when incident from the side of the substrate. Arranging the component  400  with the substrate facing the incident RHCP beam results in a focused LHCP beam  422 . 
         [0079]    For a LHCP light beam  420  in  FIG. 4B , the situation is reversed. The LHCP beam  420  is transformed into a focused RHCP beam  412  when incident from the side of the DWL and it is transformed into defocused RHCP beam  411  when incident from the side of the substrate. 
       Cylindrical DWL 
       [0080]    In the second type of diffractive waveplate lenses to which the present invention applies, illustrated in  FIGS. 5A and 5B , the orientation of the optical axis of the birefringent material of the thin film layer depends only on the linear distance x from a central axis. This type of cylindrical diffractive waveplate lens is used for applications such as focusing a beam of light to a line for imaging light from the sun onto a line of photovoltaic devices. In the paraxial approximation, the angle α that the optical axis of the birefringent material makes with the coordinate axis is given by the following equation: 
         [0000]    
       
         
           
             α 
             = 
             
               
                 ± 
                 
                   
                     k 
                     0 
                   
                   
                     4 
                      
                     
                         
                     
                      
                     f 
                   
                 
               
                
               
                 x 
                 2 
               
             
           
         
       
     
         [0000]    where k 0  and f have the same meanings as before, and x is the distance from the center of the coordinate axis.  FIGS. 5A  and B correspond to patterns of different sign (cylindrical lenses of different sign). 
       Operation for Unpolarized Light 
       [0081]    In many imaging applications, the source of light is unpolarized. In such a case show in  FIG. 6A  the DWL focuses one hand of circular polarized component of light  620  and defocuses the opposite one  610 . The power density of the defocused light  621  decreases rapidly with propagation distance and can still allow imaging for the focused portion of the light  612 . An aperture  650  can be introduced in the system as shown in  FIG. 6B  to allow propagation of the focused component while further attenuating the defocused beam propagated through the system and to the sensor. The defocused polarization can be fully blocked using a circular polarizer  660  as shown in  FIG. 6C . In realization show in  FIG. 6C , the polarizer film is integrated with the DWL and can serve as a substrate. 
         [0082]    In a particularly important application, polarized sunglasses, goggles, etc. can serve as such a substrate. Attaching DWL films  703  on circular polarizing glasses  702  may impart ophthalmic action on sunglasses, protective goggles, ski goggles, and other protective eye ware shown as  701  in  FIG. 7 . Further, a quarter wave phase retardation plate can be integrated with the DWL to be used with sunglasses that are linearly polarized. 
         [0083]    An example of uses of electrically switchable diffractive waveplate lenses of the present invention are camera lenses and machine vision wherein the contrast reduction due to presence of defocused beam does not affect required image information obtained due to focused portion of the beam. 
         [0000]    Combination with Other Functional Layers 
         [0084]    The DW lenses  801  shown in  FIG. 8 , along with other functional layers  802 , may have an adhesive backing  803  for attachment to a support sheet  804  making up a kit that incorporates many DWLs that could be detached and reattached to a different substrate such as a refractive lens. This is demonstrated in  FIG. 9  where  900  is a refractive lens,  901  is the adhesive, and  902  designates DWL with all other functional layers as required for different applications. The refractive lens can be birefringent and/or variable. 
       Vision Correction 
       [0085]    The flexibility of being able to change the properties of a diffractive waveplate lens simply by changing the pattern of the optical axis orientation in the thin film of the lens does not apply only to correcting for spherical aberrations, it applies to the other types of imaging aberrations well known in the art of optical design. Additionally, the present invention provides the opportunity of fabricating bifocal ophtalmic lenses by smooth variations of the orientation pattern in the thin film diffractive waveplate. In one embodiment of the current invention for ophthalmic uses, the flexibility of producing any desired orientation pattern can be used to inexpensively fabricate lenses fine-tuned to precisely correct eye aberrations. 
         [0086]    A very common application of optical systems is to correct for deficiencies in human vision. In this application, in common eyeglasses, a refractive lens is placed in front of each eye. The corrective optical element is fabricated from a refractive medium, such as glass or plastic in the case of eyeglasses. Eyeglasses include those that, in addition to providing refractive correction, also provide protection of the eyes from sunlight (prescription sunglasses). 
         [0087]    In order to provide vision correction, the surfaces of eyeglasses have a particular curvature, often designed specifically for the person who wears the corrective optics. It would be of value from the point of view of cost and weight to eliminate the need for surface curvature in wearable vision correction devices. Since diffractive waveplate lenses include surface layers sometimes only a few micrometers in thickness, compared to the few millimeters of thickness typical of common eyeglasses, creation of eyeglasses and other wearable optics for vision correction could be of significant value due to reduction in cost and weight. 
         [0088]    In the case of swimming goggles and goggles designed for eye protection, the requirements of the primary application may conflict with the requirement for vision correction. For example, in the case of goggles designed to protect the eyes from small high-speed moving objects, the ballistic performance of the goggles is dependent on the cross section of the optical element covering the eye. It would be highly desirable in such applications as swimming goggles and goggles designed for eye protection to be able to provide vision correction by means of thin film layers, without having to disturb the underlying structure. Diffractive waveplate lenses have the capability to allow vision correction without changing the underlying optical element, simply by applying the diffractive waveplate lenses on the surface of each goggle. 
       Intraocular Lens Application 
       [0089]    A common method of human vision correction is to insert an intraocular lens as a replacement for the biological lens of the eye. The most common reason for this replacement is to correct for the vision defects associated with cataracts. While the surgical techniques required to perform replacement of the biological lens with an artificial lens are highly developed and usually successful, the availability of an optical element that performs the same function, but in a lighter package, would provide an additional option for the refinement of this medical procedure. Since diffractive waveplate lenses, unlike conventional refractive lenses, can be very thin and yet still perform the desired function, a potentially valuable application of this technology is fabrication of such lenses, either alone or combined with other optical elements, as an intraocular replacement for the biological lens of the human eye. 
       Diffractive Waveplate Mirror 
       [0090]    While all of the exemplary embodiments discussed herein are of a realization of diffractive waveplate lenses employed in a mode in which the optical beam is transmitted through the thin film diffractive waveplate lens and through the underlying substrate, an alternative embodiment is to apply the thin film diffractive waveplate lens to a flat mirror as demonstrated in  FIG. 10 . In this manner, flat reflective optical elements can be fabricated to have a wide variety of beam deflecting properties, including the ability to focus light with a flat reflective optical element. In one of the preferred embodiments shown in  FIG. 10 , a flat mirror  1004  is coated with a quarter waveplate  1003  and a diffractive waveplate lens  1002 . A circular polarized collimated light beam  1001  is thus reflected from the system a focused beam  1105 , for example. 
         [0091]    The exemplary embodiments described herein have assumed either explicitly or implicitly that the thin film constituting the diffractive waveplate lens is applied to the flat surface of a solid substrate such as glass. Neither the assumption of a solid substrate, nor the assumption of a flat surface, should be taken as restrictive in defining the potential embodiments of this invention. As will be evident to anyone skilled in the art, the coatings may be applied to curved substrates, and to flexible substrates. All of the exemplary embodiments described herein could also be realized with either a curved substrate, a flexible substrate, or a substrate that is both curved and flexible. 
         [0092]    While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.