Abstract:
Methods and systems for solar energy converter with increased photovoltaic and thermal conversion efficiencies including a collection optics for receiving and concentrating incident sunlight, or radiation from any other directed electromagnetic energy source, an optical filtering unit for separating and redirecting infrared light and ultraviolet light from incoming solar light, a thermal distribution unit redirecting heat from the optical filtering unit into a thermal-loop, and a photovoltaic for receiving the filtered light from the filtering system and converting the light into energy.

Description:
[0001]    This application claims the benefit of priority to U.S. Provisional application No. 61/074298 filed on Jun. 20, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to solar energy collection and, in particular, to methods, apparatus and systems for solar energy conversion with improved photovoltaic efficiency, frequency conversion and thermal management permitting super highly concentrated collection of solar energy. 
       BACKGROUND AND PRIOR ART 
       [0003]    Applicant is not aware of any published material related to the use of optical fiber (in any way) in a solar energy converter. After an extensive literature search in December 2007, Applicant was able to find one paper proposing frequency conversion in a thin-film layer on top of a photovoltaic [Richards and Shalav, Synthetic Metals, 154 (2005) 61-64]. The approach described in the found literature is limited to almost single-pass conversion efficiency although some guiding can happen in a layer and it wouldn&#39;t have the many other advantages that fiber offers including thermal management, realm of super high concentration, etc. to name a few. 
         [0004]    A primary objective of the present invention is to provide methods and systems to increase the efficiency of a photovoltaic (PV) via optical filtering and concentration of the incident sunlight (or radiation from any other directed electromagnetic energy source). 
         [0005]    A secondary objective of the present invention is to provide methods and systems to frequency convert the filtered energy so that it&#39;s within the response range for photovoltaic conversion. 
         [0006]    A third objective of the present invention is to provide methods and systems to achieve the optical filtering and/or frequency conversion in conjunction with a solar thermal loop into which out-of-band energy is directed via radiative and conductive couplings. 
         [0007]    A fourth objective of the present invention is to provide methods and systems to permit operation in previously unachievable realms of super highly concentrated solar irradiance. 
         [0008]    A solar energy system with increased photovoltaic and thermal conversion efficiencies including a collection optics I-or receiving and concentrating incident sunlight, or radiation from any other directed electromagnetic energy source, an optical filtering unit for separating and redirecting infrared light and ultraviolet light from incoming solar light, a thermal distribution unit redirecting heat from the optical filtering unit into a thermal-loop, and a photovoltaic for receiving the filtered light from the filtering system and converting the light into electrical energy. The optical filtering unit can include an optical waveguide or an optical fiber selected from a group consisting of fiber, bundle of optical fibers, tapered rods, tapered fiber, photonic crystal fiber (PCF), multi-core, multi-clad, slab waveguides and hexagonal rod and can be a dielectric material or a glass material. Additionally, the optical waveguide uses one of a total internal reflection (TIR) and a transverse resonance to achieve electromagnetic confinement and guidance. The collection optics can be a Fresnel lens, a parabolic dish mirror, or a parabolic trough mirror and the entrance optics can be a window-filter, rod, tapered rod, multi-lens array, ball lens or lensed fiber. The filtering by the optical filtering unit is accomplished via at least one of the absorptive properties of the optics and the fiber, the chromatic aberration of the optics and the fiber, waveguiding and angle-tuning of the fiber to optimize the spectral transfer. 
         [0009]    The thermal distribution unit redistributes heat by at least one of a conductive coupling of the heat to the thermal loop and a radiative coupling the heat from the optical filtering unit into the thermal loop. The optical fiber can be a fiber bundle of input heads that are epoxied together, a fiber bundles of input heads that are fused together, a fiber bundles of input heads having claddings removed and cores fused together or a metallic ferrule for housing the fiber bundle of input heads and a heat sink mesh between fibers in a bundle. The thermal distribution unit can also include a coolant with the optical fibers routed through the coolant and/or a heat pipe or heat pipes arrayed in a radial arm to a ring topology to rapidly transfer thermal energy collection optics into a manifold that interfaces the coolant flow to the rest of the thermal loop. The coolant, heat pipe or heat pipes arrayed in a radial arms to a ring topology are thermally insulated and can an evacuated glass tube. 
         [0010]    The system can also include a frequency converter to convert a ultraviolet and a infrared radiation to a visible band that the photovoltaic is responsive to. In this example, the optical fibers in the bundle have claddings to form cladding pumped fiber amplifiers and can include a mirror and a fiber Bragg grating coupled to both ends of the optical fibers to form cladding pumped fiber lasers. The inner conduction tube can also form a single fiber amplifier with waveguiding of the amplifier providing a preferred direction for the re-radiation of the solar pumped molecules or atoms undergoing stimulated emission of radiation and a mirror at an ends of the inner conduction tube enhancing the direction for a stimulated emission, turning the amplifier into a laser. The laser is end pumped by one of a Fresnel lens and a dish mirror or side pumped by a trough mirror and grating at top of tube providing distributed feedback DFB eliminating mirrors at end of tube. The frequency conversion is resonantly enhanced in an optical resonator can be a fiber ring resonators incorporating couplers, a fiber ring resonators incorporating hybrid fiber/bulk-optics modules, a reflective resonators incorporating optical circulators and a fiber Bragg grating FBG and a mirror or a fiber based resonator. 
         [0011]    In an embodiment, the collector includes a concentrated light beam source is one of an array of mirrors in a solar farm, a solar pumped lasers from one of a terrestrial, satellite, or platforms in the solar system, the collector receiving the concentrated light beam 
         [0012]    Further objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments which are illustrated schematically in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0013]      FIG. 1   a  shows lens implementations of the solar energy system according to the present invention. 
           [0014]      FIG. 1   b  shows an example using solar energy converter using coolant tubes and heat pipes. 
           [0015]      FIG. 2  shows an example using solar energy converter using entrance optics and insulated or evacuated tubes. 
           [0016]      FIG. 3   a  is a front view of an end-fired tube. 
           [0017]      FIG. 3   b  is a top view of  FIG. 3   a  showing the use of more coolant tubes and heat pipes and a ring manifold which represents coupling to the remainder of the thermal loop. 
           [0018]      FIG. 4   a  shows an interfacing to a parabolic dish mirror. 
           [0019]      FIG. 4   b  shows an alternate interfacing to a parabolic dish mirror 
           [0020]      FIG. 4   c  shows an interfacing to a hybrid lens-trough collector. 
           [0021]      FIG. 4   d  shows an interfacing to a multi-lens array. 
           [0022]      FIG. 5  shows a solar pumped fiber/tube amplifier/laser 
           [0023]      FIG. 6   a  shows a side pumped fiber/tube amplifier/laser with a parabolic trough mirror collection optics. 
           [0024]      FIG. 6   b  shows a side pumped tube amplifier/laser of  FIG. 6   a  with a fiber interface. 
           [0025]      FIG. 6   c  is a side-view of the tube amplifier/laser with a distributed feedback DFB grating structure at the top of the tube. 
           [0026]      FIG. 6   d  is an alternate side-view of the tube amplifier/laser showing the mirror/grating reflecting the non-absorbed energy at an angle grater than the critical angle to confine the energy inside the fiber/amplifier/laser. 
           [0027]      FIG. 7  shows a fiber ring resonator according to the present invention. 
           [0028]      FIG. 8  shows a reflective resonator in a linear topology utilizing an optical circulator. 
           [0029]      FIG. 9  shows an example using hybrid fiber/bulk-optics beam-splitter modules. 
           [0030]      FIG. 10   a  shows an edge-fired photovoltaic with fiber delivery to the band-gap and solid electrodes. 
           [0031]      FIG. 10   b  shows an example using conductors that have an approximately same area as the photovoltaic disk to remove the electricity. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its application 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. 
         [0033]    The following is a list of the reference numbers used in the drawings and the detailed specification to identify components:
     14  WDM coupler     15  nonlinear fiber or fiber/bulk nonlinear optics     16  optical isolator     17  fiber Bragg grating     20  fiber Bragg grating or fiber/bulk mirror     30  optical circulator     31  parabolic trough mirror     33  tube     40  mirror     43  fiber/bulk beam splitter module     47  collection optics     48  multi-lens array     49  heat sink     51  outer tube     52  heat pipe     53  thermal conduction tube     54  coolant     55  insulating material     56  fiber input head or ferrule     61  valve     63  ring manifold     71  fiber input structure     72  sunlight     73  entrance optics     77  fiber bundle or optical waveguide     91  Fresnel lens     92  fiber bundle     93  fiber group/legs     210  current     211  electrodes     212  PN junction     213  multiple fibers     214  conductors     215  PV material   
 
         [0068]    Use of the phrase “optical fiber” herein generally refers to any such optical waveguide of any dielectric, glass, or other material of any size including rods, lightpipes, fiber bundles, multi-mode fiber, single-mode fiber, etc.; and of any shape, including but not limited to, tapered rods, tapered fiber, photonic crystal fiber (PCF), multi-core, multi-clad, slab waveguides, hexagonal rod, etc. Most of optical fibers utilize total internal reflection (TIR) to achieve electromagnetic confinement and guidance of a mode, but photonic crystal fibers and photonic band-gap guides achieve this via mechanisms other than total internal reflection, for example a transverse resonance which has been likened to the way gratings operate. The present invention employs any of these technologies and generally refers to them as “fiber.” 
         [0069]    Fiber provides numerous alternative methods and systems for performing optical filtering, frequency conversion, and thermal energy distribution, permitting high levels of solar concentration from collection lenses and/or mirrors before passing the in-band energy onto the photovoltaic cells and/or PV systems. 
         [0070]    The collection optics can be Fresnel lenses, parabolic dish mirrors, parabolic trough mirrors etc., including the option of utilizing secondary entrance optics and windows for interfacing to the fiber and the solar thermal loop without deviating from the scope of the invention. Any choice of collection optics offers its own filtering aspects via absorption, reflection and chromatic aberration which can be optimized in conjunction with the choice of fiber and/or entrance optics. Due to the flexibility of the fiber&#39;s routing and heat transfer properties, the solar thermal loop could be one of many configuration, including but not limited to, absorption chillers Stirling engines, thermo-electric converters, steam engines; etc., depending primarily on the scale, the size and number of optical collection modules, and referred to generically as the “thermal loop.” 
         [0071]    The configuration in the first set of examples, do not explicitly utilize frequency conversion arising from non-linear optical interactions within the fiber, although UV absorption and re-radiation as heat can be considered as a type of frequency conversion. The fiber can perform filtering and transfer ultraviolet UV and infrared IR energy into the thermal loop via radiative and/or conductive couplings. The first few examples illustrate the use of the fiber in a conductive coupling mode of operation in which the fiber absorbs UV and IR creating heat which is conducted into the thermal loop. The later examples illustrate the use of the fiber in a manner that also utilizes a radiative coupling mode of operation in which the IR is detuned from the multimode entrance angle of the waveguide, so that less of the IR propagates through the fiber and more of the IR is coupled directly into the thermal loop. 
         [0072]    The first example of the solar energy system is shown in  FIG. 1 . The ultraviolet and infrared light, and the band that the photovoltaic has appreciable responsivity to, all undergo multi-mode propagation. For silicon the band is approximately 400 nm to approximately 1125 nm and is referred to herein the “visible” light. In this example, there is no waveguide filtering or angle tuning of these modes, just the filtering effects of the material response of the fiber, i.e., the absorption, re-radiation and conduction of the resulting heat into the thermal loop. 
         [0073]    In the configuration shown in  FIG. 1 , the collection optics of a module is a Fresnel lens  91  and the fiber is a bundle  92  of optical fibers. For small lenses, less than approximately 0.5 m diameter, the bundle&#39;s input head  56  inside the metallic ferrule can contain epoxies capable of withstanding relatively low temperatures less than approximately 500 degrees C. For large lenses, greater than approximately 0.5 m diameter, the bundle&#39;s input head can contain optical fibers that have been fused together, forming a water tight seal capable of withstanding approximately 1600 degrees C., which is the melting point of most glass fibers, e.g., those similar to silica dioxide. 
         [0074]    The bundle of fiber collects the solar energy at the “hot spot” focused by a Fresnel lens then each fiber, or groups of fibers  93 , referred to as “legs,” in the bundle can snake out in many directions, over long or short distances, throughout the thermal loop. Thus providing efficient heat transfer into the coolant, as the heat conducts into the coolant further along the fiber. Moreover, the scalability can be a significant feature. With fibers of low optical loss there is virtually no limit on the length of the fibers, so they can be used to make the efficiency of the heat transfer extremely high. 
         [0075]    Even with standard telecommunication grade fiber, where the losses are greater at wavelengths near the 850 nm peak responsivity of silicon than the losses are at telecommunication wavelengths near 1550 nm, these larger losses (2 dB/km compared to 0.2 dB/km) are still manageable since, transcontinental lengths are not envisioned for most solar applications. Only approximately a one meter length of fiber is needed to route the light to the photovoltaics on the side of a one meter diameter lens with reasonable bends for negligible bend loss in the fiber. Moreover, fiber attenuation “losses” that are changed into heat are not lost, instead they couple back into the thermal loop. As shown in  FIG. 1   a,  the interface to the thermal loop could take place via an array of lenses on a container of any shape, such as the rectangular shape shown, or via lens modules that interface to coolant  54  carried by tubes  51  that house the fiber and/or fiber input heads  56  as shown in  FIG. 1   b.    
         [0076]    Since the power to the photovoltaic is delivered by fiber, the photovoltaic can be placed upstream in the coolant of the thermal loop where it is cooler than at the hot spot where the energy strikes the fiber bundle, or the fiber can transport the energy to photovoltaics located entirely outside the thermal loop. The hot spot can be located inside the coolant and at a depth that creates an anti-reflective AR coating effect on the incident energy. Reflection losses at the fiber input can be further reduced via the simultaneous use of a Brewster angle and a quarter-wave transformer layer and/or via a standard AR coating on the fiber input head. Chromatic dispersion of the focusing lenses and/or the collecting mirrors can be used to focus the infrared and/or the ultraviolet more into the coolant and the remainder of the light more into the fiber. Heat pipes  52  can also be employed to rapidly transfer thermal energy from the hot spot into the remainder of the thermal loop. 
         [0077]    The configuration shown in  FIG. 1   a  does not employ entrance optics, e.g., windows, so the filtering effects rely primarily upon the fiber. Thus a one meter length of ultraviolet fused silica makes an attractive choice with transmission of approximately 99.8% of the light near 800 nm where silicon photovoltaics have large responsivity while attenuating over approximately 20% of the infrared at approximately 1200 nm and beyond. 
         [0078]    The second example shown in  FIG. 2  uses entrance optics and a tubular coolant/thermal-loop topology. The entrance optics  73  can mitigate thermal stresses on the coolant aperture by making it a larger area than the fiber bundle input head. This could take the form of tapered rods, or more simply using of the area reduction from the primary collection lens as the beam passes through an entrance optics window as shown in  FIG. 2 . The window&#39;s inherent filtering characteristics can also be utilized to enhance the filtering of the fiber. This also frees up some cost effective choices among fiber types. For example, relatively inexpensive borosilicate fiber which provides less infrared to visible suppression could be used instead of the more expensive ultraviolet fused silica fiber if the entrance optics window provides some of the filtering; while it also conducts into the coolant before the remaining heat is coupled into the fiber which further conducts heat into the coolant as it channels the useful visible light out of the thermal collector and onto the remotely located photovoltaic. 
         [0079]    Chromatic aberration of the entrance optics window can also be used to adjust the spectral coupling into the fiber bundle input head instead of into the coolants in the same way the chromatic aberration of the primary lens can be used. The tube can include an outer tube  51  surrounding a thermally insulating material  55  which surrounds an inner thermal conduction tube  53 . The thermally insulating material  55  could also be a vacuum. 
         [0080]    An alternative configuration illustrates how tradeoffs between fiber length and coolant/thermal-loop technology can lead to larger scale modules, efficiently delivering higher levels of visible light and heat transfer from a larger lens or mirror. These configurations can employ evacuated tubes that are commercially available and used in pre-existing solar thermal systems because the vacuum provides greater thermal isolation than any material. Although normally laid flat in the sun, in this example they are end-fired, as shown in  FIG. 3   a,  from the collection optics with the fiber routed down the inner thermal conduction tube  53  with or without entrance optics  73 . 
         [0081]    The inner thermal conduction tube  53  can be metal or glass that is coated with a black material to further absorb ambient radiation from the sides. This inner conduction tube  53  can contain coolant flowing in a variety of different configurations without deviating from the scope of the invention as shown. The coolant inputs and outputs would typically be symmetric, coming from both sides as shown in  FIG. 3   a  or coming from four or more sides as shown in  FIG. 3   b  which shows a top view of this alternative configuration. As shown, heat pipes  52  can help transfer heat out of the hot spot at the fiber input head  56  and the ring manifold  63  represents thermal conduction of the heat pipes  52  and coolant tubes to the remainder of the thermal loop. Valves  61  can be used to select alternate directions of coolant flow while still maintaining back-pressure to prevent turbulence and air bubbles for various temperature ranges of operation and the ring topology permits the use of the type of heat pipes that require elevation, independent of the module&#39;s orientation while tracking the sun. 
         [0082]    The system shown in  FIG. 4  includes the components described for the previous examples with the option of alternate collection optics.  FIGS. 4   a  and  4   b  show two different configurations for interfacing the fiber to parabolic dish mirror  74  collection optics. The first example shown in  FIG. 4   a,  shows that the incoming sunlight  72  can be strongly coupled via proper arrangement of the fiber input structure  71 . The configuration shown in  FIG. 4   b  shows that shadowing can be minimized by stringing the fiber further away from the focal point. 
         [0083]    In either configuration, the fiber can be routed upstream and/or downstream in flexible coolant tubes although the figures show the fiber routed in only one direction.  FIG. 4   c  illustrates a hybrid trough-lens system topology in which a Fresnel lens with a large amount of chromatic aberration focuses the visible light onto the fiber bundle while leaving the infrared relatively unfocused so that the infrared passes on to the parabolic trough mirror  31  which focuses the infrared onto the collection tube  33  of the thermal loop.  FIG. 4   d  illustrates how, with any of the primary collection optics  47  topologies, such as lenses, dish, or trough, secondary entrance optics can take the form of multi-lens arrays  48  to focus on the individual fibers, or legs  93 , of a fiber bundle  92 . This permits greater spacing between the fibers, or legs, for optical and thermal optimizations. Therein a metallic honey-combed array/heat-sink  49  can hold the fibers into the bundle and quickly conduct “front-end” thermal energy into the coolant  54 . This honey-combed array/heat-sink  49  could be fabricated by chemical deposition techniques and the spacing between the fibers in the bundle  92  readily optimized for various applications. 
         [0084]    Frequency conversion via processes found in lasers, such as the stimulated emission of radiation, SER, is illustrated in the example of  FIG. 5 . In some applications the claddings of the fibers in the bundle can be removed and the cores fused at the input head of the bundle to maximize optical transfer into the cores; however, if the claddings are not removed, then they can be utilized to form cladding pumped fiber amplifiers  44 . The waveguide or fiber amplifier can be turned into a lasers, by putting mirrors or fiber Bragg gratings, FBGs,  20  on the ends of the waveguide or fibers as shown in  FIG. 5 . 
         [0085]    Referring to  FIG. 6  in conjunction with  FIGS. 3 and 5 , is a similar configuration in that, the entire inner conduction tube  33  can function as a single fiber functioning as a single amplifier; and/or by including mirrors: a single laser. Since a critical angle could still be maintained at the tube to air, or tube to vacuum, interface, even if the tube is filled with fluorescent dyes, like Rhodamine 6G for example, the waveguiding of the amplifier provides a preferred direction for the re-radiation of the solar pumped molecules or atoms. This preferred direction for the stimulated emission can also be enhanced through the use of mirrors at the ends of the tube to turn the amplifier into a laser. Since this is true even if the tube is side pumped instead of end pumped, this also permits the incorporation of a parabolic trough mirror collection optics topology  31  as shown in  FIG. 6   a.    
         [0086]    The conduction tube  33 , now a fiber and/or amplifier and/or laser, can be housed in an insulating tube  120 , possibly an evacuated tube, as in  FIG. 6   b,  with lenses and/or mirrors at each end which allow coolant and/or fluorescent dyes to flow into tubing  121  which couples to the remainder of the thermal loop. The light exits via windows, in a manner similar to the entrance optics previous described, and/or via fiber which can be used to couple thermal energy to the tubing  121  and/or filter the light before passing it on to the PVs. A side-view of the trough  134  is provided in  FIG. 6   c  illustrating how the incident light  131  cans pass into the bottom  133  of the tube and any non-absorbed radiation can be reflected from a mirror and/or grating structure  130  at the top of the tube. 
         [0087]    The alternate side-view of  FIG. 6   d  shows how the mirror/grating can reflect the non-absorbed energy at an angle grater than the critical angle thereby confining the energy to remain inside the fiber/amplifier/laser. The critical angle of either interface, the inner tube to insulating region, or insulating region to air, can be used, however a wave-optics perspective (rather than ray-optics perspective) provides insight as follows. The grating need not be triangular in shape, nor metallic, and can be simply etched on the tube; the grating sets up a coupling of waveguide modes and thereby creates a distributed-feedback (DFB) structure, similar to that utilized in DFB lasers. This thereby eliminates the need for any mirrors at the end of the fiber/amplifier/laser tube. 
         [0088]    In addition to the absorption and conductive coupling properties of the fiber, the guidance condition in optical fibers and radiative couplings can also act as a filter to separate and distribute the visible and the infrared radiation. The higher frequency visible light, corresponding to the band to which the photovoltaic has the highest responsivity, can be set for multi-mode propagation corresponding to a wider set of acceptable input angles while the lower frequency infrared is set for single-mode propagation. By tuning the angle of incidence to the fiber, the infrared can be effectively decoupled while the coupling of the visible is relatively unaffected. Similar to the conductive coupling into the coolant of the fiber&#39;s absorbed ultraviolet and infrared, this radiative coupling also provides efficient heat transfer into the coolant as the partially-guided/leaky-modes of the infrared continue to radiate further along the fiber. Standard telecommunication grade single mode fiber, which is single-mode at wavelengths near 1550 nm, would be multi-mode at wavelengths of approximately 850 nm, where silicon photovoltaics have a peak response. As a result, inexpensive, readily available fiber can be used. 
         [0089]    Another example uses nonlinear optical processes in fiber and/or other components to up-convert the infrared into the visible response band of the photovoltaic. The chromatic aberration of the collection optics and/or entrance optics, or fiber and the absorptive filtering of the fiber or optics, and/or the angle tuning as described in the preceding paragraph, can be used to adaptively, or statically, optimize the amount of infrared that is sent down the fiber for subsequent up-conversion versus the amount that is radiated into the coolant, or in the case of no thermal loop, radiated into free space. The absorption and chromatic aberration of the optics and fiber would statically optimize the spectral transfer initially, then the aberration and angle tuning are readily optimized dynamically by simply moving the fiber longitudinally or rotationally, respectively. The angle tuning and chromatic aberration optimizations could also adapt to ambient conditions such as brightness, coolant temperature, time of day and demand for hot water. 
         [0090]    Non-standard fiber to further maximize the heat transfer, in a novel way, can alternatively be employed. The material and thickness of the fiber cladding can be selected to match the infrared wave impedance of the coolant, similar to a “quarter-wave transformer.” The spectral range of such a fiber thermal quarter-wave transformer can be broadened by longitudinally modulating the index of refraction of the cladding along the fiber. Alternatively the cladding thickness can be modulated, but the manufacturing of index modulation is readily achieved via ultraviolet photo-etching as in manufacturing fiber Bragg gratings. Fiber Bragg gratings can be used throughout the system, and/or in front of the photovoltaic, to reflect and transfer, via fiber wavelength division multiplexing couplers, any residual infrared not already utilized elsewhere. 
         [0091]    Chromatic dispersion, also known as chromatic aberration, of the collection optics can be used for filtering purposes, as described in regard to the example shown in  FIG. 1 , but it can similarly be used to optimize the amount of blue light coupled into the fiber for subsequent frequency down-conversion and to mitigate the potential of ultraviolet photo-etching of the fibers or damage to the silicon. Note that this can be done in conjunction with the angle tuning of the fiber, and the absorptive filtering aspects of the fiber, to filter out any harmful UV from the enormous energy potential of down-converting the rest of the blue light. Likewise, chromatic dispersion, angle tuning, fiber thermal quarter-wave transformers, and other techniques for maximizing heat transfer into the thermal loop—can also be used to optimize the amount, and the spectrum, of the infrared to be coupled and propagated into the fiber for subsequent frequency up-conversion. 
         [0092]    Alternatively, or additionally, frequency conversion can be achieved via any number of, or combinations of, a wide variety of nonlinear optical processes. Resonators can be used to enhance the net efficiency of the frequency conversion process in one or more of the alternative examples previously described. For example, in a second-order (chi-two) process the amount of the frequency converted field is proportional to the square of the incident field. Thus the efficiency of the chi-two conversion itself is proportional to the incident field. Similarly the efficiency of chi-three conversion is proportional to the square of the incident field. Therefore, even if the single-pass conversion in a nonlinear material, such as a fiber, might be small (e.g., say approximately 4%), close to 100% conversion can be achieved by putting the nonlinear material (possibly fiber) in a resonator (possibly a fiber ring resonator) because the field inside the resonator is larger by a factor of approximately 1/(1−r) where r; the reflectivity of the resonator mirrors (or input/output couplers) can be made very close to one. Simply put, whatever doesn&#39;t get converted in one pass, gets converted in a later pass because it can not get out of the resonator, or ring, until it is converted and output from the frequency selective mirrors (or wavelength division multiplexing couplers). 
         [0093]    Fiber ring resonators provide a cost-effective topology that maintains the thermal distribution advantages of fiber. The fiber ring resonators can be long, or short, loops of nonlinear fiber or fiber/bulk nonlinear optics  15 , fusion-spliced to wavelength division multiplexing couplers  14 . Optical isolators  16 , which are also available in fiber format, can be employed to ensure unidirectional energy rotation in the ring, and FBGs  17  can be used to prevent any residual undesired frequencies from passing on to the photovoltaic, as illustrated in  FIG. 7 . Shorter loops of fiber could also be used if they have higher nonlinearities and/or if the resonator enhancement is sufficient. 
         [0094]    Nonlinearities that can be incorporated into this class of embodiments abound in a variety of fiber, including, but not limited to the following. Second harmonic generation which could provide the infrared up-conversion in PCFs and/or other types of fiber which break the inversion symmetry so that a chi-two process can take place. Virtually any non-isotropic structure or material would suffice, including PCFs, multi-core and/or multi-clad fiber, waveguides with a strong surface wave component. Third and higher-order harmonic generation for up-conversion of the infrared. Parametric down-conversion could down-convert the blue and the UV. Stimulated Raman scattering can also provide and/or contribute to down-conversion. Four-wave mixing processes can be used for up-conversion when used in conjunction with other processes, down-conversion and/or a combined frequency mixing of IR and UV components to produce output frequencies in the visible range. 
         [0095]    Some of the energy in the ring, or any other resonator, can excite thermal transitions and these could be coupled into the coolant. Fiber based resonators, including ring resonators, are particularly efficient in providing the thermal distribution. Each ring can be spaced with respect to the other rings, after snaking out from the bundle, the hot spot, to maximize the transfer of undesired heat into the coolant. Likewise, components Within each ring can be positioned per thermal constraints. Moreover, the concentrator can be a honeycomb of Fresnel lenses etched into the plastic or glass that covers the coolant of the thermal loop. Each lens would focus into a fiber bundle that can be suspended in the coolant flow by supports and/or the tension of the fiber and rings connected to the photovoltaic located upstream or remotely, outside of the thermal loop. 
         [0096]    The example shown in  FIG. 8  replaces the use of a coupler with an optical circulator  30 . The resonator takes on a linear topology instead of the ring previously described, and includes a fiber Bragg grating or fiber coupled to a bulk optics mirror  20  which reflects the desired visible band back to the circulator which routes it the visible light to the photovoltaic and passes the out-of-band frequencies into the resonant cavity formed by the two mirrors  20  and  40  and the nonlinear fiber or fiber/bulk nonlinear-optics  15 , as illustrated in  FIG. 8 . 
         [0097]      FIG. 9  illustrates a means of removing the out-of-band frequencies from the light that passes onto the photovoltaic, which does not require couplers or circulators and fiber Bragg gratings. It also shows a possible method of combining the energy from several modules, each with their own collection optics.  FIG. 9  illustrates the combination of two such modules. These configurations provide the relatively large solar bandwidths desired via hybrid fiber/bulk-optics beam-splitter modules  43 . The input and output ports of these modules have fiber connectors, or are fusion spliced to fiber. Lenses, possibly ball lenses, inside the modules expand or contract the beam waists to interface to a bulk-optics beam-splitter or a partially transmitting frequency selective mirror. 
         [0098]    Such multi-layered dielectric mirrors include a highly developed industry in bulk-optics and often offer higher bandwidths and higher power capabilities relative to their fiber-optics counterparts, at least relative to many of those that are currently commercially available. Yet, outside the module the energy is still in fiber (with its inherent thermal distribution capabilities) and the entire system can still be immersed in coolant. Each module can feed into its own frequency conversion unit, or they could be combined to feed into a single conversion unit, as shown in  FIG. 9  which shows the ring resonator topology. The coupler  42  can be eliminated entirely, replacing it with a linear resonator topology similar to the example shown in  FIG. 8  or by simply replacing it with a single-pass frequency conversion unit. 
         [0099]    In any of the previously described examples, the collector can receive an already concentrated beam of light from mirror arrays in a solar farm, from solar pumped lasers (via terrestrial, satellite, or platforms elsewhere in the solar system), or from any other directed energy source. 
         [0100]    In any of the previously described examples, especially in the super highly concentrated applications, the thermal loop can be replaced by an inexpensive and readily scaleable thermal dump, like a swimming pool, pond, lake, or even an ocean. Since fiber losses can be quite small there is virtually no limit as to the length of these fibers. For example, witness the transoceanic distances in telecommunication systems and the fact that we also can employ optically pumped fiber amplifiers. Hence we can also employ long fiber lengths and make the efficiency of the heat transfer extremely high. Thus, we also offer a system that although huge, is inexpensive, and capable of converting an immensely intense optical beam into useful electricity. 
         [0101]    Even in the super highly concentrated applications, a thermal loop can be utilized, and water would make an eco-friendly coolant. The heat engine can be a simple steam engine, possibly driving even a simple paddle-wheel type of electric generator and the mechanical energy that gets lost as heat is not really lost, since that could be coupled back into the thermal loop. 
         [0102]    Fiber also provides novel options for the illumination of the photovoltaic, a simple example being the arrangement of fibers to provide uniform illumination of the surface of a standard photovoltaic cell or an array of cells. In the super highly concentrated realms applications, the delivery of energy from the fiber to the photovoltaic can be accomplished in an edge-fired topology. The photovoltaic is essentially a PN junction  212 , similar to that of a diode. This junction can be large, like a large flat disk, and the fiber bundle or rod can splice out into multiple fibers  213 , each of which could deliver optical energy to points around the edge of the junction, approximately perpendicular to the huge current  210  that it generates, as illustrated in  FIG. 10   a.    
         [0103]    The multiple fibers along the edge impact different paths/locations within the junction while the huge current is reduced to a manageable current density by the surface area of the disk. Moreover, that area can now be totally covered by electrodes  211 , on both sides of the photovoltaic, thus dramatically reducing the ohmic losses. Additionally, ohmic losses can further plummet by making the conductors  214  that remove the electricity the same area as the electrodes, the same area of flat side of the photovoltaic disk as shown in  FIG. 10   b.  The electrodes and/or conductors can also provide heat removal and redirection to couple any thermal transitions in the photovoltaic into the thermal conversion loop or thermal dump. 
         [0104]    An edge-fired fiber/photovoltaic topology can also be used to mitigate the non-photovoltaic interactions between the optical field and the bulk of the photovoltaic material  215  and its electrodes, thereby reducing heating, dislocation, deformation and other high intensity damage processes. In some applications it would be cost-effective to use superconducting cabling at the photovoltaic site until these high currents can fan out into several standard power station cables. Note in passing that any two-photon and multi-photon transitions in the photovoltaic are still exciting electrons up into the conduction band, and that any undesirable photo-dislocation, mechanical deformation, type of transitions have been mitigated by control through filtering and conversion of the ultraviolet and infrared spectrum of the energy before it impinges onto the photovoltaic. 
         [0105]    Lastly, in standard roof-top applications, fiber, most likely with inexpensive Fresnel lens or parabolic dish mirror concentrators can simply deliver heat and light to the inside of a building directly rather than to a photovoltaic or thermal loop during periods of external sunshine. The fiber core diameter can be set to provide partially-guided/leaky-modes in the visible range for the routing of indoor lighting and angle-tuning and/or longitudinal adaptation of the chromatic aberration could dynamically control the brightness and the amount of heat coupled into the building. 
         [0106]    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.