Abstract:
An optical concentrator having a concentrating element for collecting input light, a redirecting element for receiving the light and also for redirecting the light, and a waveguide including a plurality of incremental portions enabling collection and concentration of the light onto a receiver. Other systems replace the receiver by a light source so the optics can provide illumination.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation-in-part and claims priority from U.S. patent application Ser. No. 12/705,434, filed Feb. 12, 2010, which is a continuation of U.S. Pat. No. 7,664,350, filed Sep. 9, 2008, which is a continuation-in-part of U.S. Pat. No. 7,672,549, filed Sep. 10, 2007, all of which are incorporated herein by reference in their entirety. 
     This invention is directed to an optical concentrator for producing electrical, thermal and radiative energy, and also to an optical illuminator employing the structure and methods described hereinafter. More particularly, the invention is directed to a solar concentrator using a combination of optical elements to concentrate and aggregate sunlight. Other applications include lighting and illumination using the compact optics. 
    
    
     BACKGROUND OF THE INVENTION 
     Solar collectors have long been developed for the collection and concentration of sunlight. Increasing the energy density of ambient sunlight enables more efficient conversion to useful forms of energy. Numerous geometries and systems have been developed, but the mediocre performance and high costs of such systems do not permit widespread use. In order to achieve adequate performance and manufacturability, improvements in solar energy collectors are needed. 
     SUMMARY OF THE INVENTION 
     A concentrator system includes a combination of optical elements comprising a concentrating element, such as a refractive and/or reflective component, a reflective and/or refractive element to redirect sunlight into a light waveguide which is constructed with a plurality of stepped reflective surfaces for efficient aggregation and concentration into a receiver unit (thermal and/or photovoltaic) and other conventional energy conversion systems. The control of the geometry of the reflective surfaces along with the aspect ratio of the light waveguide enables ready manipulation, collection and concentration of sunlight preferably onto a contiguous area for a variety of commercial applications, including solar cell devices, light pipe applications, heat exchangers, fuel production systems, spectrum splitters and other secondary manipulation of the light for various optical applications. These structures and methods can also be applied advantageously for a wide variety of optical illumination applications. 
     These and other objects, advantages and applications of the invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a solar energy concentrator generally constructed in accordance with an embodiment of the invention; 
         FIG. 2  illustrates a cross-sectional view of one embodiment of a light waveguide shown schematically in  FIG. 1 ; 
         FIG. 3  illustrates another cross-sectional view of a linear embodiment of a light waveguide shown schematically in  FIG. 1 ; 
         FIG. 4  illustrates another cross-sectional view of a rotational embodiment of a light waveguide shown schematically in  FIG. 1 ; 
         FIG. 5A  shows a first edge shape of a reflecting element of a waveguide;  FIG. 5B  shows a second edge shape for a reflecting element of a waveguide;  FIG. 5C  shows a first separate element for redirecting light as part of a stepped waveguide; FIG.  5 D shows a second separate element for redirecting light as part of a stepped waveguide;  FIG. 5E  shows a system with plural light pipes coupled to a stepped waveguide and  FIG. 5F  shows a waveguide with embedded redirecting components; 
         FIG. 6  shows a curved concentrating element and curved reflector coupled to a waveguide; 
         FIG. 7  shows a curved concentrating element and two planar reflectors coupled to a waveguide; 
         FIG. 8A  shows a closed optical element coupled to a waveguide and  FIG. 8B  shows an enlarged view of a portion of  FIG. 8A  at the juncture of the optical element and waveguide; 
         FIG. 9A  shows another closed optical element coupled to a waveguide and  FIG. 9B  shows an enlarged view of a portion of  FIG. 9A  at the juncture of the optical element and the waveguide; 
         FIG. 10A  shows another closed optical element coupled to a waveguide and  FIG. 10B  shows an enlarged view of a portion of  FIG. 10A  at a juncture of the optical element and the waveguide; 
         FIG. 11A  shows a further closed element coupled to a waveguide and  FIG. 11B  shows an enlarged view of portion of  FIG. 11A  at a juncture of the optical element and the waveguide; and 
         FIG. 12  shows ray tracing results for the optical systems of FIGS.  2  and  6 - 11 . 
         FIG. 13  illustrates another representation of an embodiment of a solar energy concentrator or an illuminator; 
         FIG. 14  illustrates a refractive concentrator component for a conventional system; 
         FIG. 15  illustrates a reflective concentrator component for another conventional system; 
         FIG. 16  illustrates a Cassegrainian concentrator having a primary and secondary reflective optic; 
         FIG. 17  illustrates light transmission versus acceptance angle for a system like  FIG. 13 . 
         FIG. 18  illustrates an embodiment where the waveguide ends with a reflector component for redirecting light towards a base surface; 
         FIG. 19  illustrates a variation on  FIG. 18  where the concentrator is mirrored about an axis of symmetry; 
         FIG. 20  illustrates a form of the embodiment of  FIG. 13  with the waveguide and redirecting elements tilted relative to the concentrators; 
         FIG. 21  illustrates an embodiment with varying size of concentrator and/or redirecting element; 
         FIG. 22  illustrates an embodiment for light diffusion using a light source in place of a receiver; 
         FIG. 23  illustrates a different variation on the embodiment of  FIG. 4  to achieve light concentration across two axes; 
         FIG. 24  illustrates yet another embodiment to achieve concentration across two axes; 
         FIG. 25  illustrates a different embodiment of a solar concentrator of the invention; 
         FIG. 26  illustrates yet another embodiment of a solar concentrator of the invention; 
         FIG. 27  illustrates a further embodiment of a solar concentrator of the invention 
         FIG. 28  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 29  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 30  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 31  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 32  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 33  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 34  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 35  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 36  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 37  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 38  shows a waveguide with entry elements; 
         FIG. 39  illustrates a different embodiment of a waveguide with entry elements; 
         FIG. 40  illustrates a different embodiment of a solar concentrator of the invention; 
         FIG. 41  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 42  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 43  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 44  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 45  illustrates a different embodiment of an optical concentrator of the invention; 
         FIG. 46  illustrates a different embodiment of a solar concentrator of the invention with symmetry about a central axis; 
         FIG. 47  shows an extruded view of  FIG. 46  with positioning elements; 
         FIG. 48  illustrates examples of transverse optical elements and positioning elements; 
         FIG. 49  shows an extruded view of  FIG. 46  with transverse optical elements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A solar energy concentrator system constructed in accordance with a preferred embodiment of the invention is indicated schematically at  10  in  FIG. 1 . The solar energy concentrator system  10 , includes an optical concentrating element  12  which can be any conventional optical concentrator, such as an objective lens, a Fresnel lens, and/or a reflective surface element, such as a parabolic or compound shaped reflector. This optical concentrating element  12  acts on input light  14  to concentrate the light  14  to a small focal area  16 . In the preferred embodiment, the small focal area  16  is disposed within reflective or redirecting component  18 , or other conventional optical redirecting element which causes total internal reflection. The redirecting component  18  redirects the concentrated light  20  into a waveguide  22 . The waveguide  22  is constructed to cause internal reflection of the light  20  which propagates along the waveguide  22  in accordance with Snell&#39;s law wherein total internal reflection occurs when the angle of the light  20  incident on surface  24  of the waveguide  22  is greater than the critical angle, Ø c :
 
Ø c =sin(η waveguide /η cladding )
         Where Ø c =critical angle for total internal reflection,   η waveguide =refractive index of waveguide material   η cladding =refractive index of a cladding layer or the index at the ambient/waveguide interface.       

     A receiver  26  is disposed at the end of the waveguide  22  and receives the light  20  for processing into useful energy or other optical applications. 
       FIG. 13  illustrates a preferred form of the system  10  with details of this mechanism. A plurality N of concentrating elements  12  and redirecting elements  18  are shown. Each of the concentrating elements  12  takes the input light  14  with a half angle of θ 1  from an area A, and concentrates the light  14  to a smaller area B with half angle θ 2 , such that Concentration Ratio=A/B. Each of the redirecting elements  18  receives the concentrated light from an associated one of the concentrating elements  12 , rotates it by some angle φ, and inserts it into a section of the waveguide  22 , preserving the level of concentration defined by area B and half angle θ 2 . The waveguide  22  is a plurality of sections having incremental steps of height B that are spaced from each other by length A. Each section of the waveguide  22  receives light from an associated one of the redirecting elements  18 , such that the waveguide  22  as a whole aggregates light from the plurality of the concentrating elements  14  and the redirecting elements  18 , and propagates the light  14  along its length for collection by a receiver  23 . The waveguide  22  does not change the level of concentration delivered to it, and therefore the aspect ratio of the waveguide  22   
     
       
         
           
             
               
                 
                   = 
                   
                     height 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     of 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       waveguide 
                       / 
                       length 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     of 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     waveguide 
                   
                 
               
             
             
               
                 
                   = 
                   
                     N 
                     × 
                     
                       B 
                       / 
                       N 
                     
                     × 
                     A 
                   
                 
               
             
             
               
                 
                   = 
                   
                     B 
                     / 
                     A 
                   
                 
               
             
             
               
                 
                   = 
                   
                     
                       1 
                       / 
                       Concentration 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ratio 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     in 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     each 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     element 
                   
                 
               
             
           
         
       
     
     Compactness has great practical benefits for solar concentrators (and other devices such as illuminators). Among other benefits: less material is used, large air gaps between optics and the receiver  23  that need difficult sealing are eliminated, devices are much less bulky for cheaper shipping and installation, traditional flat module manufacturing methods can be utilized as opposed to expensive and risky custom manufacturing methods. 
     The limit of compactness for the waveguide  22  is defined by the receiver  23 . Thus, the waveguide  22  can only be as compact as the receiver  23  to which it delivers light. For most concentrators, the compactness of the concentrator  12  is significantly larger than the width of the receiver  23 . However, since this device constructs the waveguide  22  from sections each having height defined by the area of concentrated light delivered to it, the aggregated waveguide  22  has a height equal to the width of the receiver  23 . In other words, the waveguide  22  is at the limit of compactness. 
     Therefore in view of the construction of the invention, the concentration of light achieved by the concentrator system  10  being a function of the aspect ratio A/B leads to a highly compact concentrator system  10 . The device can aggregate light from a relatively wide area and concentrate it to a relatively small receiver that has a contiguous area while remaining highly compact. This simplifies production by reducing the volume of material required, allowing for multiple units to be made from a single mold and reducing assembly complexity. 
       FIG. 12  shows the results of ray tracings performed on the designs depicted in FIGS.  2  and  6 - 11 . Each design demonstrates a particular performance in terms of its ability to concentrate light in the linear dimension, as shown by the ratio of A/B. The data is for light having an input cone half angle of +−1 degree, an output cone half angle of +−20 degrees, an initial refractive index of n=1, and a final refractive index of n=1.5. The theoretical maximum allowable concentration of light with those input parameters is 30× in the linear dimension, whereas  FIG. 9  for example achieves a concentration factor of 25×. Since the concentration factor in the linear dimension is proportional to the aspect ratio A/B, the design shown in  FIG. 9  can deliver a concentrator that is 250 millimeters long (A) while only 10 millimeters in thickness (B); or a concentrator that is 500 millimeters long (A) while only 20 millimeters in thickness (B). This represents a highly compact concentrator system  10  that can effectively aggregate concentrated light from a relatively wide area and deliver it to a single receiver. 
     The dimensions and number of the concentrating elements  12  and redirecting elements  18  can be varied for any entry aperture of the concentrator  12 . For example, the system  10  shown in  FIG. 13  can be achieved with twice as many elements (2×N) of half the size (A/2 and B/2). As the concentrating elements  12  and the redirecting elements  18  become smaller and more numerous, the aspect ratio of the entire concentrator  12  approaches the aspect ratio of the waveguide  22 , given by 1/Concentration Ratio. In other words, for a Concentration Ratio of 10, the aspect ratio of the concentrator  12  can be 0.1. 
     Typical aspect ratios for concentrators  12  are on the order of 1.  FIG. 14  shows a refractive concentrator  12 , which may be, for example, an objective lens or a Fresnel lens. The focal length of an objective lens defines the height  25 . The Concentration Ratio is given by A/B, whereas the aspect ratio is given by height/A, which is larger than the Concentration Ratio.  FIG. 15  shows a similar situation for a reflective form of the concentrator  12 . 
     Attempts have been made to reach the limit of compactness for a single concentrating element.  FIG. 16  shows a Cassegrainian concentrator composed of a primary and secondary reflective optic. The aspect ratio given by Height/A is 0.25. Winston, in “Planar Concentrators Near the Etendue Limit”, 2005, describes the “fundamental compactness limit of a 1/4 aspect ratio.” In the context of the invention, this compactness limit applies to an individual one of the concentrating elements  12 . The use of the waveguide  22  that aggregates light from multiple ones of the concentrating elements  12  is what allows the compactness of the system  10  to go lower than ¼ and approach 1/Concentration Ratio. 
     The invention also has advantages in the transmission efficiency of light energy from input to delivery to the receiver  23 . In  FIG. 13 , θ 2  is controlled by the concentrating element  12 . θ 2  also becomes the angle made by the light hitting the surface of the waveguide  22 , and 90−θ 2  is the angle made with respect to the normal of the waveguide surface. As discussed above, θ 2  can be set to achieve total internal reflection within the waveguide  22 , reducing surface absorption losses to zero. 
     In addition, the concentrating element  12  and redirecting element  18  can be designed to manipulate the light  14  using total internal reflection, as shown in specific embodiments below. Also, the concentrating element  12  and redirecting element  18  and the waveguide  22  can be designed to provide a contiguous path within a solid dielectric medium for the light  14 . In other words, light rays from the input region to the receiver  23  need never encounter either a reflective coating or a change in refractive index. Reflective coatings can cause absorption losses of ˜8%. A change in refractive index from an optical material of refractive index 1.5 (plastic or glass) to air can cause Fresnel reflection losses of ˜4%. Transmission efficiency with respect to these loss mechanisms can therefore approach 100%. 
     This is in contrast to conventional concentrator optics. Reflective optics will have 8% loss per reflection. Transmission efficiency will therefore be ˜92% for a single optic, and ˜85% when a secondary reflective optic is used. Refractive optics require at least one change in refractive index. Transmission efficiency will therefore be ˜96% for a single optic, and ˜92% when a secondary refractive optic is used. 
       FIG. 17  shows transmission as a function of input half angle θ 1  through the embodiment of the invention shown in  FIG. 13 . The calculation is based on ray tracing software. The embodiment was designed to function within input angles of +−3 degrees. The efficiency takes into account losses from Fresnel reflections and hard reflections. As is shown, the efficiency of the device approaches 100% at θ 1 =0 degrees, stays near 100% within +−3 degrees, and then drops off sharply. 
     In another preferred form of the concentrator system  10  shown in  FIG. 2 , the incident light  14  is concentrated or focused in a first step using the element  12  described hereinbefore. The concentrated light  20  is further processed by associating sections of the concentrator system  10  with reflector/waveguide sections  28 . Each of the reflector/waveguide sections  28  comprises a reflective section  32  which receives the concentrated light  20  and redirects light  30  within the associated waveguide section  28  with the light  30  undergoing total internal reflection (TIR) along the length of the entire waveguide  22 . A plurality of the reflector/waveguide sections  28  comprise the waveguide  22  and forms a stepped form of waveguide construction. 
       FIG. 18  shows another embodiment of the system  10  where the waveguide  22  ends in a reflector  27  that redirects the light  14  towards the base surface of the waveguide  22 , where the receiver  23  may be placed. It can be of manufacturing benefit to have the concentrator optics be laid down flat onto a plane of conventional receiver elements which embody the receiver  23 . 
     With this construction, the concentrator  12  can be mirrored about an axis of symmetry as shown in  FIG. 19 , such that the two receivers  23  from either end form one contiguous area where one single receiver  23  may be placed. In this case, since the aperture area is doubled but the thickness of the concentrator  12  unchanged, the limit of compactness is given by 1/(2× Concentration Ratio). 
     The redirecting element  18  rotates the light paths by an angle φ. In  FIG. 13 , φ is shown to be 90 degrees.  FIG. 20  depicts φ&lt;90 degrees. This can allow, as one benefit, the concentrating elements  12  to be located on the same plane, and the redirecting elements  18  on their own plane as well, which can aid manufacturability. 
     The concentrating element  12  and the redirecting element  18 , and associated waveguides  22 , may also vary in size and  FIG. 21  shows an example of this. Here A1, A2, and A3 are different lengths, as are B1, B2 and B3. However, the Concentration Ratio stays the same in each section: A1/B1=A2/B2, and so on. The aspect ratio of the waveguide  22  is therefore still given by 
     
       
         
           
             
               
                 
                   = 
                   
                     
                       ( 
                       
                         
                           B 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         + 
                         
                           B 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         + 
                         
                           B 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           3 
                         
                       
                       ) 
                     
                     / 
                     
                       ( 
                       
                         
                           A 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         + 
                         
                           A 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         + 
                         
                           A 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           3 
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     
                       1 
                       / 
                       Concentration 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ratio 
                   
                 
               
             
           
         
       
     
     In another embodiment shown in  FIG. 22 , the system  10  can also be utilized as a light diffuser by running light  31  through it in reverse. In  FIG. 22 , light input from a light source  33  that was originally the receiver  23 , is channeled through the waveguide  22 , redirected by the redirecting element  18  onto the concentrating element  12 , which delivers the output light above the system  10 . Applications include illumination, backlighting, and other light diffusing devices. It should be understood throughout that optics illustrated for concentration of light can also be used for illumination with the “receiver  23 ” being replaced by a light source. 
     The cross-section of the various reflector/waveguide sections  28  provides a basic building block for various configurations of the concentrator system  10 . One exemplary commercial embodiment is shown in  FIG. 3  with an aspect ratio N×B/N×A, A/B, an area concentration factor or energy density ΔØ which is proportional to A/B where N×A is the length of the waveguide  22  and N×B is the largest thickness (see  FIGS. 2 and 3 ). In a most preferred embodiment, the thickness N×B is comprised of a plurality of incremental step heights, B, which provide a clear light pathway for TIR light from each of the reflector/waveguide sections  32 . 
       FIG. 4  illustrates another example of the concentrator system  10  in the form of a rotationally (or axially) symmetric geometry having a concentrator system  10 ′ and the concentrating element  12  in association with the reflector/waveguide sections  28  of the waveguide  22 . This rotationally symmetric form of the concentrator system  10 ′ (or the system  10 ), which can be any portion of a full circle, enables three dimensional radial convergence of the incident light  14  resulting in ΔØ the Concentration Ratio being proportional to (A/B) 2  thereby substantially enhancing collection and concentrator efficiency. In a most preferable embodiment of  FIG. 4  two axis solar tracking is used as opposed to the single axis tracking for the embodiment of  FIG. 3 . 
       FIG. 4  shows one way to achieve concentration across two axes, and  FIG. 23  shows another way. Here, a linearly symmetric primary concentrator  12  delivers light concentrated along one axis to its receiver  23  at the side of a concentrator  12 . There, a second linearly symmetric concentrator  37  is positioned in the perpendicular axis. This secondary concentrator  37  concentrates light along the second axis, bringing the light to the final receiver  23 . 
       FIG. 24  shows a third way to achieve concentration across two axes. Here the concentrators  12  shown are of the mirror symmetry as described in  FIG. 19 . Again, a linearly symmetric primary concentrator  12  delivers light  14  concentrated along one axis to its receiver  23  at the base of the concentrator  12 . There, a second linearly symmetric concentrator  37  is positioned in the perpendicular axis. This secondary concentrator  37  concentrates the light  14  along the second axis, bringing the light to the final receiver  23 . 
     In addition to the linear and rotational embodiments of  FIGS. 3 and 4 , the concentrator system  10 ′ can be disposed both above and/or below the waveguide  22  relative to the direction of the incident light  14 . In such embodiments, some of the light  14  will pass through the waveguide  22  and be redirected back to the waveguide  22  by the concentrator system  10 ′. These forms of systems enable light recycling and thus improve end efficiency and the use of the reflective systems for concentration, described herein, show an increased efficiency for concentration of light relative to conventional refractive system. 
     In other embodiments, the reflective elements  18  can be angularly adjusted with respect to the waveguide  22  in order to cause TIR. The reflective element  18  can be an integral part of the waveguide  22  with a variety of angular profiles (see  FIGS. 5A and 5B ). The element  18  also can be separate elements  38  and  39  (see  FIGS. 5C and 5D ). In addition, the reflective element  18  and the associated waveguide  22  can also take the form of complex light collector pipes  42  and light redirecting components  43  as shown in  FIGS. 5E and 5F , respectively. 
     The above described forms of the concentrator system  10  and  10 ′ provide concentrated light  20  to a contiguous area as opposed to a nodal area, thereby allowing delivery of concentrated solar energy to a variety of downstream receivers  26 , such as a solar cell, a light pipe for further processing, a heat exchanger, a secondary concentrator and a light spectrum splitter. 
     In yet another series of embodiments shown in  FIGS. 6-11B , a variety of optical components can be used in combination to further and substantially enhance both the concentration and collection efficiency.  FIG. 6  in a most preferred embodiment shows a curved concentrating element  50  directing light  52  onto a curved reflector  54  which passes the light  52  into the waveguide  22 .  FIG. 7  in another most preferred embodiment shows another curved concentrating element  56  which directs the light  52  off a reflector  58  having two planar surfaces  59  and  60  which redirect the light  52  by TIR into the waveguide  22 .  FIG. 8A  shows a partially closed optical element  64  which redirects the light  52  at interface  66 , reflects the light  52  off curved reflector  68  focusing the light  52  onto interface  70  between a bottom reflective surface  72  of the optical element  64 . As best seen in the enlarged view of  FIG. 8B , the waveguide  22  has a substantially complementary angular match to the reflective surface  72 . 
     In  FIG. 9A  in another most preferred embodiment is a similar system as in  FIG. 8A , but the optical element  65  is closed and coupled to an extension waveguide  74  (a form of light pipe) which collects the light  52  and transmits it into the waveguide  22  (as best seen in  FIG. 9B ). 
     In  FIG. 10A  an optical element  76  is closed with the input light  52  reflected by TIR from reflective surface  77  with a particular angular cross section best shown in  FIG. 10B  which enables collection of the light from TIR and coupling with the waveguide  22  from reflection off surfaces  80 ,  81  and  82 . 
     In  FIG. 11A  an optical element  82  cooperates with another reflector  84  to direct the light  52  into the waveguide  22  from the two different optical sources  82  and  84 , thereby further ensuring collection of all the light incident on surface  86  of the optical element  82 . In this embodiment the optical elements  82  and  84  perform the role of both concentrating elements and reflecting elements. 
     In  FIG. 25 , a curved concentrating element  12  directs the light  14  onto (the redirecting component  18 ) which passes the light  14  into the waveguide  22 . The concentrating element  12  and the redirecting component  18  are shown as two different features on the same physical part, while the waveguide  22  is shown as a second physical part coupled to the first. In  FIG. 26 , a curved concentrating element  12  directs the light  14  onto two reflectors (the redirecting component  18 ) acting in sequence which pass the light  14  into the waveguide  22 . The concentrating element  12 , the redirecting component  18 , and waveguide  22  are all shown as separate physical parts coupled together.  FIG. 27  directs the light  14  into the waveguide  22  similar to  FIG. 26 . However, the redirecting component  18  and the waveguide  22  are combined into one construction. 
     In  FIG. 28 , a refractive concentrating element  12  directs the light  14  onto a redirecting element  18  which reflects the light  14  into the waveguide  22 . The redirecting elements  18  are preferably integrated into the waveguide structure as incremental step features. In  FIG. 29 , the concentrating elements  12  and redirecting elements  18  are similar to those in  FIG. 28 , but the top surface of the waveguide  22  is angled so that the waveguide  22  has a substantially uniform cross-sectional thickness along its length. 
       FIG. 30  is similar to  FIG. 29 , except that the redirecting elements  18  and the waveguide  22  are rotated such that the waveguide is substantially parallel to the plane of the concentrating elements  12 .  FIG. 31  is similar to  FIG. 30 , except with an additional set of redirecting elements  87  that refract the light from the concentrating elements such that the incident angle of light onto redirecting element  18  is larger than the comparable incident angle of light in  FIG. 30 . This, for example, better facilitates total internal reflection as the mechanism of redirection for the redirecting element  18 .  FIG. 32  is similar to  FIG. 31 , except the top surface of the waveguide  22  is a tailored shape  88 . The tailored shape  88  is useful for example in delivering the light propagating through the waveguide to a defined spot or location L at the end of the waveguide  22 . 
     In  FIG. 33 , the redirecting elements  18  are integrated into a single part that is separate from the parts carrying the concentrating elements  12  and the waveguide  22 . The redirecting element  18  may be of any type previously described in this application, and is shown as a curved reflective element similar to that in  FIG. 6 . The waveguide  22  is comprised of incremental step features  89  which are positioned to receive the light from the redirecting elements  18 .  FIG. 34  is similar to  FIG. 33 , except that the base surface  90  of the waveguide  22  is angled so that the waveguide has a substantially uniform cross-sectional thickness along its length.  FIGS. 35 and 36  show the base surface of the waveguide  22  are of tailored shapes  88 , shown as flat facets  88  and a curved element  88  respectively. As in  FIG. 32 , the tailored shape  88  is useful for example in delivering the light propagating through the waveguide  22  to a defined spot L at the end of the waveguide  22 . 
       FIG. 37  is similar to  FIG. 30  except that the concentrating element  12  is a Fresnel lens. The Fresnel lens may be manufactured for example by injection molding, hot embossing or microreplication of polymeric materials or other materials suitable to those processes. 
       FIG. 38  shows a waveguide  22  with entry elements  91  on the top surface, similar to those in  FIG. 33-36 .  FIG. 39  shows a similar waveguide  22 , except that the entry elements  91  are integrated as a separate part, which is then optically attached to the flat top surface of the bulk waveguide element  22  via an optical coupling layer  92 . The light entry elements are therefore physically discontinuously disposed from the body of the waveguide. This allows the use of for example manufacturing processes based on thin film substrates to make the entry element features.  FIG. 40  shows the waveguide  22  shown in  FIG. 39  operating within an example of a full optical design. A concentrating element  12  concentrates light  14  onto a redirecting element  18 , which redirects the light  14  for insertion into the waveguide  22  via the entry elements  91 . 
       FIG. 41  is similar to  FIG. 30 , except that the part containing the concentrating elements  12  is optically coupled to the waveguide  22  using a low index adhesive  93 . This construction eliminates an air gap between the concentrating elements  12  and the waveguide  22 , and therefore diminishes optical losses due to the Fresnel reflection effect as light travels from the concentrating elements  12  to the waveguide  22 . The low index adhesive  93  needs to be of an appropriate refractive index, lower than the refractive index of the waveguide  22 , in order to enable propagation of light within the waveguide  22  using total internal reflection. The low index adhesive  93  may for example be a silicone elastomer such as Dow Corning Sylgard 184.  FIG. 42  is similar to  FIG. 41 , except that the concentrating element  12  is a Fresnel lens rather than an asymmetric bulk lens. 
     In  FIG. 43 , the concentrating element  12  directs the light  14  to a first redirecting element  87  that refracts the light  14 , directing the light  14  onto the second redirecting element  18 , which redirects the light into the waveguide  22  for propagation. In  FIG. 43 , the first redirecting element  87  is a flat facet.  FIG. 44  is similar to  FIG. 43 , except that the first redirecting element  87  interacts with light  14  prior to the concentrating element  12 . In  FIG. 45 , the waveguide  22  propagates light  14  bi-directionally or in multiple directions across its length. The concentrating element  12  concentrates light onto redirecting elements  18  and  94 , with the two redirecting elements  18  and  94  redirecting the light in opposing directions into the waveguide  22 . This construction allows light to be concentrated and collected at both ends of the waveguide  22 . 
     In  FIG. 46 , the concentrating element  12  concentrates the light  14  onto the redirecting element  18 . The redirecting element  18  has two parts, a flat facet  95  which refracts the light into the bulk optic, and another flat facet  96  which reflects the light into the waveguide  22 . The redirecting facets  95  and  96  and the waveguide  22  are integrated into a single part. The end of the waveguide has a facet  99  that redirects the light downwards towards the receiver  23 , as previously described in para [0059]. In this embodiment, the waveguide  22  has the waveguide  97  as its mirror image about axis  98 . The placement of secondary optics at the end of the waveguide  22  and the symmetric layout of waveguides  22  can be implemented with all embodiments shown in this application, and has been previously explained in para [0049]. 
     The redirecting elements  18  described in  FIG. 1-46  are associated with corresponding concentrating elements  12 , and transfer light into the waveguide  22  utilizing at least one of the optical mechanisms of reflection, total internal reflection, and refraction. The redirecting elements can be but need not be optically coupled with and physically separate from the concentrating elements. 
     In the various embodiments described above in this application, the concentrating element  12  is separated from at least a portion of the associated redirecting element  18  by a layer. The light  14  does not undergo any repositioning change of direction within this layer. The layer itself is contiguous between at least a portion of each of the associated redirecting elements  18 . This separating layer enables the concentrating elements  12  and redirecting elements  18  to be disposed in a vertical stack of physically separate components. This enables direct assembly of separate parts to form the overall solar concentrator. 
     In order to minimize cost and simplify design, one practical challenge is to achieve all the functionality described above in as few parts as possible with robust materials. Generally, this involves incorporating multiple functions into only a few parts. For instance, by patterning optical features into a coverglass it is feasible to enable the glass to both protect the module and act as the concentrating element  12  while preserving its ability to act as a substrate for various optical coatings. By applying a cylindrical metal roll with machined concentric features to softened glass, large glass manufacturing facilities can routinely form mild lens features on one side of a sheet Given the proper roll design to impress optical features, linear lenses may be patterned on the coverglass to form the primary optic (concentrating) element  12 . The concentrating element  12  can be oriented in both outward and inward facing directions while preserving functionality. Outward facing features run the risk of particulate accumulation, also known as soiling, which is detrimental to light transmission. In addition to manipulated coverglass approaches, features can be added to a flat coverglass using processes such as silicone deposition which also provide concentrating functionality. 
     Further, it is possible to construct a complementary secondary optical part that serves as the redirecting element  18  for the concentrated light  14  from the coverglass layer and act as the waveguide  22  to deliver the redirected light  14  to the receiver  23  ( FIG. 46 ). Note that in this embodiment the primary optic serves as both the protective coverglass and concentrating layer while the redirecting and waveguide functions can be combined in the secondary optic. Similarly, for point-focus designs, an axially symmetric lens pattern may be applied to glass using a hot embossing or mold-type process. 
     Incorporating optical functionality into the coverglass and combining the redirecting and waveguide-to-focal-area functionality into one part enables the entire optical path to be managed or achieved by only two parts. One critical aspect of this two-part class of ATIR optics is that both the vertical and horizontal position of the waveguide or secondary optic must be well maintained relative to the primary optic layer (coverglass). In other terms, maintaining the geometry of the separating layer is critical to ensuring robust functionality. One way to achieve this is by incorporating yet another function within either the primary or secondary/waveguide optical parts. For instance, as shown in  FIG. 47 , by incorporating a positioning element, or rib feature,  100  into the secondary optic, it is possible to mechanically interlock the primary and secondary optic parts, constraining them in both the vertical and horizontal dimensions to ensure a stable separation. The positioning element  100  therefore maintains geometrical relationships between the plurality of optical elements and the waveguide in the horizontal, vertical, and rotational planes. 
     Another option for production is to create a separate supporting positioning element or rib feature  100 . This option carries the disadvantage of having to make another separate part. However, the rib feature is so simple that the tooling cost for molding this part can be low, and the assembly becomes more modular—allowing design flexibility in the way that ribs and secondary optic parts are assembled.  FIG. 48  shows renderings illustrating complimentary optical secondary and support rib feature  100 . These parts can be assembled in a modular fashion to provide design flexibility. The positioning element  100  can therefore be either an integral part of the waveguide or a separate element from the waveguide. 
     It is likely that a viable receiver may consist of multiple discrete photovoltaic solar cells. When stringing solar cells together it is advisable to leave a gap between cells to manage stress concentrations around solder joints and minimize cell breakage. The effect of these gaps is to reduce the area from which light energy may be gathered. These gaps are useful locations for positioning non-optically-active support features such as the positioning elements or ribs  100 . Also, the optic may be adapted with an optical redirecting element, or notch feature,  101  so as to direct the majority of light that would have otherwise fallen onto the gap towards active receiver ( FIG. 49 ). The notch feature  101  is similar to a redirecting element but oriented in a different plane of the waveguide  22  so as to internally reflect light away from gaps and onto an active receiver. The notch or transverse optical element  101  is coupled to the waveguide  22  and redirects the light in the transverse direction to the direction of propagation of light within the waveguide  22 . Previously, secondary optical elements  27  have been described which couple to the waveguide and redirect light from the waveguide to the light receiver. When the above-mentioned transverse optical elements  101  are utilized, the secondary optical elements  27  redirect light from the waveguide and from the transverse optical elements to the light receiver. 
     The foregoing description of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.