Patent Publication Number: US-6912018-B2

Title: Electro-optical glazing structures having total-reflection and transparent modes of operation for use in dynamical control of electromagnetic radiation

Description:
RELATED CASES 
     This application is a continuation of application Ser. No. 09/354,192, filed Jul. 15, 1999, now U.S. Pat. No. 6,583,827 and is a Continuation-in-part of: application Ser. No. 08/739,467 entitled “Super Broadband Reflective Circularly Polarizing Material And Method Of Fabricating And Using Same In Diverse Applications”, by Sadeg M. Faris and Le Li filed Oct. 29, 1996 now U.S. Pat. No. 6,034,753, which is a Continuation-in-Part of application Ser. No. 08/550,022 entitled “Single Layer Reflective Super Broadband Circular Polarizer and Method of Fabrication Therefor” by Sadeg M. Faris and Le Li filed Oct. 30, 1995 now U.S. Pat. No. 5,691,789; application Ser. No. 08/787,282 entitled “Cholesteric Liquid Crystal Inks” by Sadeg M. Faris filed Jan. 24, 1997 now U.S. Pat. No. 6,338,807, which is a Continuation of application Ser. No. 08/265,949 filed Jun. 27, 1994 now U.S. Pat. No. 5,599,412, which is a Divisional of application Ser. No. 07/798,881 entitled “Cholesteric Liquid Crystal Inks” by Sadeg M. Faris filed Nov. 27, 1991, now U.S. Pat. No. 5,364,557; application Ser. No. 08/715,314 entitled High-Brightness Color Liquid Crystal Display Panel Employing Systemic Light Recycling And Methods And Apparatus For Manufacturing The Same” by Sadeg Faris filed Sep. 16, 1996 now U.S. Pat. No. 6,188,460; and application Ser. No. 08/743,293 entitled “Liquid Crystal Film Structures With Phase-Retardation Surface Regions Formed Therein And Methods Of Fabricating The Same” by Sadeg Faris filed Nov. 4, 1996 now U.S. Pat. No. 6,133,980; each said Application being commonly owned by Reveo, Inc, and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to an electro-optical glazing structure having total-reflection and semi-transparent and totally-transparent modes of operation which are electrically-switchable for use in dynamically controlling electromagnetic radiation flow in diverse applications. 
     2. Brief Description of the Prior Art 
     The use of windows in homes, commercial buildings, and automotive vehicles alike is very well known. The reasons for providing windows in such structures and systems are directly related to the functions they perform. For example, window structures provide for ventilation, lighting, a sense of spaciousness, as well as a way of making contact with the outdoors. Windows made of glazing (e.g. glass material) also permit selective transmission of electromagnetic radiation between the outdoors and the interior space of homes, commercial buildings, and automotive vehicles. While conventional forms of glazing serves many useful functions, such forms are not without problems. 
     An appreciation of the problems presented by the use of conventional glazing in windows, can be most easily attained by recognizing the nature and composition of electromagnetic radiation with which windows universally come in contact. 
     On a clear day at sea level, electromagnetic radiation is composed of 3% ultraviolet light (i.e. electromagnetic radiation in the UV band), 44% visible light (i.e. electromagnetic radiation in the visible band), and 53% infrared light (i.e. electromagnetic radiation in the IR band). In accordance with the laws of physics, 50% of all electromagnetic radiation produced is left hand circularly polarized (LHCP) while the other 50% thereof is right hand circularly polarized (RHCP). The total electromagnetic radiation striking a window surface is a combination of direct radiation from the Sun and diffuse radiation from the ambient environment. While electromagnetic radiation is broad-band in nature, it is the ultraviolet light component thereof which causes molecular decomposition in various types of plastic material and inorganic dyes, which results in color fading. 
     When electromagnetic radiation strikes a glass window, three different physical processes occur. Some of the radiant energy is transmitted through the glass; some of the radiant energy is reflected off the glass; and a small portion of the radiant energy is absorbed by the glass. The energy transmitted through the glass window is typically absorbed by furnishings or structures within the interior environment, and often becomes trapped therewithin causing an increase in interior temperature. 
     Depending on the season, electromagnetic radiation transmitted through glass windows can be either mitigate or worsen the thermal loading imposed upon the heating and cooling systems associated with the glass windows. Consequently, during the hot weather season, it is highly desired to shield windows and sliding glass doors from electromagnetic radiation in order to lessen thermal loading upon cooling systems. During cold weather season, it is highly desired to expose windows and sliding glass doors to electromagnetic radiation in order to lessen thermal loading on heating systems. 
     In short, it is highly desired to selectively control the transmission of electromagnetic radiation through window structures at different times of the day and year so that thermal loading upon the heating and cooling systems of residential, commercial and industrial building environments can be minimized. By minimizing such thermal loading, power can be used in an economical manner to control the internal temperature of residential, commercial and industrial building environments. Achievement of this goal would impact the natural environment in a positive manner, while improving the quality of life. 
     With such objectives in mind, great effort has been expended in recent times to improve the ways and means of selectively controlling the transmission of electromagnetic radiation through window structures. 
     One approach to electromagnetic radiation control involves using a window shade to reduce the transmission of electromagnetic radiation through windows. The most popular type of shade is the window blind. However, as window blind is mounted within the interior of the building or transportation environment, electromagnetic radiation is allowed transmit through the window, raise the temperature within the internal environment, and thus increase thermal loading on cooling systems during the hot weather season. Also, the operation of window blinds requires mechanical or electromechanical controls which tend to be bulky and expensive to manufacture, install and maintain. 
     Another approach to electromagnetic radiation control involves the use of sun control films which are physically applied to the surface of glass windows in building and automotive vehicles alike. Presently a variety of different types of sun control film are marketed by various firms. Such electromagnetic control films can be categorized into one of the three basic categories, namely: high reflectivity film; heat saving or winter film; and fade protection film. 
     High reflectivity electromagnetic films are most effective at blocking summer heat. The higher the reflectivity of electromagnetic film, the more effective it will be at blocking electromagnetic radiation. Electromagnetic reflectivity film having a silver, mirror-like surface is more effective in blocking electromagnetic radiation than the colored, more transparent films. Electromagnetic reflectivity films can lower the U-value of glass by more than 10%. Notably, in climates having long heating seasons, the use of high reflectivity film prevents using the winter sun to warm the interior of buildings during the cold weather season, and thus lessen thermal loading on building heating systems. 
     Heat-saving or winter films are designed to reduce winter heat losses through glazing. These films can lower the U-value of glass windows by more than 20%. 
     Fade-protection films are designed to filter out ultraviolet rays. 
     Ultraviolet rays cause about 60-65% of color fading in most home furnishing fabrics and automobile dash boards. 
     While electromagnetic radiation control films of the types described above can be used to control heat and glare, eliminate sun damage, and to a lesser extent, reduce visibility into buildings during the daytime. The major disadvantages thereof are reduction in interior light, loss of visibility, and extra care required in cleaning. Moreover, prior art electromagnetic window films are incapable of changing from transmissive during winter months to reflective during summer months in order to effectively use electromagnetic radiation for dynamic temperature control of biological environments (e.g. human habitats, greenhouses and the like). 
     An alternative approach to electromagnetic radiation control involves using special glass panels having radiation transmission characteristics which effectively absorb (i.e. block) the infrared and ultra violet wavelengths, while transmitting the visible wavelengths thereby allowing window viewing and day light to enter the interior spaces of buildings using such window technology. While the light transmission characteristics of such glass provides a measure of electromagnetic radiation control during cooling seasons, where outdoor temperatures tend to be above 72 degrees Fahrenheit, its IR absorption characteristics prevents, during heating season, IR wavelengths of Sun light to warm the interior spaces of building structures in which such glass panels are installed. Consequently, during heating seasons, such glass fails to lessen the thermal loading on the heating systems of such buildings, as would be desired in an effort to conserve energy and heating resources during the winter months. 
     In recent times, there has been great interest in using variable light transmission glass or glazing, referred to as “smart windows”, to achieve electromagnetic radiation (i.e. energy) control in buildings and vehicles alike. The reason for using smart window structures, rather than conventional glass window panels, is quite clear. Smart window structures have light transmission characteristics that can be electrically controlled during the course of the day (or year) in order to meet lighting needs, minimize thermal load on heating and/or cooling systems, and provide privacy within the interior spaces of buildings and vehicles alike. 
     The use of chromogenic switchable glazing or smart windows for controlling the flow of light and heat into and out of a glazing according to occupant comfort, is discussed in great detail in the following papers: “Chromogenic Switchable Glazing: Towards the Development of the Smart Window” by Carl Lempert published in the June 1995 Proceedings of the Window Innovation Conference, Toronto, Canada; and “Optical Switching Technology for Glazings” by Carl Lempert published in Thin Solid Films, Volume 236, 1993, pages 6-13, both incorporated herein by reference. 
     In general, there are several different types chromogenic switchable glazing or smart windows, namely: non-electrically activated switchable glazings; and electrically-activated switchable glazings. The non-electrically activated types of chromogenic switchable glazing are based on: photochromics, thermochromics and thermotropics. The most common electrically-activated types of chromogenic switchable glazing are based on polymer dispersed liquid crystals (PDLC), dispersed particle systems (DPS), and electrochromics. 
     Prior art smart window structures based upon conventional twisted nematic (TN) or super twist nematic (STN) liquid crystal technology require the use of a pair of polarizers. This, however, results in high optical loss, as up to 60% of the incident light is absorbed by the polarizers, in the desired non-blocking mode of operation. 
     While a smart window structure based on polymer dispersed liquid crystal (PDLC) technology offers better performance than TN or STN based window structures, such smart window structures suffer from several significant shortcomings. In particular, conventional PDLC panels have a translucent state which can be used only to provide privacy, but lack a totally opaque state and a totally reflective state required for electromagnetic radiation control functions. In addition, the viewing haze limitation provided by the PDLC panels prevents clear viewing through this prior art window structure at larger viewing angles. 
     A primary drawback associated with Dispersed Particle Systems is that such systems simply do not have a reflection mode of operation, and thus created heat build-up within interior spaces which is sought to be avoided in thermal radiation control applications. 
     Thus it is clear that there is a great need in the art for an improved form of variable light transmission glazing structure which avoids the shortcomings and drawbacks of prior art technologies. 
     OBJECTS AND SUMMARY OF THE PRESENT INVENTION 
     Accordingly, a primary object of the present invention is to provide an electro-optical glazing structure which avoids the shortcomings and drawbacks of prior art technologies. 
     Another object of the present invention is to provide an electro-optical glazing structure which has total-reflection, semi-transparent and totally transparent modes of operation for improved control over the flow of electromagnetic radiation within the solar region of the electromagnetic spectrum (i.e. Solar Spectrum). 
     A further object of the present invention is to provide such an electro-optical glazing structure, in which the modes of operation can be electrically-activated or switched, while avoiding the use of energy absorbing mechanisms. 
     A further object of the present invention is to provide such an electro-optical glazing structure having a broad band of operation, including the IR, visible and UV portions of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a certain polarization state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over the electromagnetic region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a linear polarization state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over the electromagnetic region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a linear polarization state, one is parallel to other, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over the electromagnetic region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a linear polarization state, one is perpendicular to other, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over the electromagnetic region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive cholesteric liquid crystal (CLC) electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a LHCP state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over the electromagnetic region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive CLC electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of a RHCP state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over a broad-band region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive CLC electromagnetic radiation polarizing panels, one of which is capable of reflecting electromagnetic radiation of the LHCP state and the other of which is capable of reflecting electromagnetic radiation of the RHCP state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over a broad-band region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising an electrically-passive π-phase retardation panel interposed between a pair of electrically-active CLC electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of the LHCP state, whereby a totally reflective state of operation and a totally transparent state of operation are provided over a broad-band region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical structure, comprising an electrically-passive π-phase retardation panel interposed between a pair of electrically-active CLC electromagnetic radiation polarizing panels, both of which are capable of reflecting electromagnetic radiation of the RHCP state, whereby a totally reflective state of operation and a semi-transparent state of operation are provided over a broad-band region of the electromagnetic spectrum. 
     A further object of the present invention is to provide an electro-optical glazing structure, comprising a pair of electrically-active CLC electromagnetic radiation polarizing panels, one of which is capable of reflecting electromagnetic radiation of the LHCP state and the other of which is capable of reflecting electromagnetic radiation of the RHCP state, whereby a totally reflective state of operation and a totally transparent state of operation are provided over a broad-band region of the electromagnetic spectrum. 
     Another object of the present invention is to provide an actively-controlled window or viewing panel constructed from the electro-optical glazing structure of the present invention, wherein the transmission of electromagnetic radiation can be dynamically controlled over a broad-band region of the electromagnetic spectrum, between 50% transmission to 100% reflection and between 100% transmission to 100% reflection. 
     Another object of the present invention is to provide an actively-controlled window or viewing panel constructed from the electro-optical glazing structure of the present invention, wherein the transmission of electromagnetic radiation over the UV and IR regions of the electromagnetic spectrum can be totally reflected, rather than absorbed, reducing the temperature cycle range which the window structure is required to undergo. 
     Another object of the present invention is to provide an actively-controlled window or viewing panel constructed from the electro-optical glazing structures of the present invention, wherein only UV and IR radiation is reflected at the window surface, while electromagnetic radiation over the visible band is transmitted to the interior environment being maintained under thermal control. 
     Another object of the present invention is to provide an intelligent window system for installation within a house Or office building, or aboard a transportation vehicle such as an airplane or automobile, wherein the electro-optical glazing structure thereof is supported within a prefabricated window frame, within which are mounted: a electromagnetic-sensor for sensing electromagnetic conditions in the outside environment; a battery supply for providing electrical power; a electromagnetic-powered battery recharger for recharging the battery; electrical circuitry for producing glazing control voltages for driving the electrically-active elements of the electro-optical glazing supported within the window frame; and a micro-computer chip for controlling the operation of the battery recharger and electrical circuitry and the production of glazing control voltages as required by a radiation flow control program stored within the programmed microcontroller. 
     A further object of the present invention is to provide such an electro-optical window structure which is designed for integration within the heating/cooling system of a house, office building, factory, or vehicle in order to control the flow of broad-band electromagnetic radiation through the electro-optical window structure, while minimizing thermal loading upon the heating/cooling system thereof. 
     Another object of the present invention is to provide a thermal/viewing shield or panel made from electro-optical glazing structure of the present invention. 
     Another object of the present invention is to provide of an intelligent pair of sunglasses, in which each optical element is realized using an electro-optical glazing structure of the present invention, fashioned to the dimensions of a sunglass frame. 
     Another object of the present invention is to provide of an intelligent pair of shutter glasses, in which each optical element is realized using an electro-optical glazing structure of the present invention, fashioned to the dimensions of a shutter glass frame. 
     Another object of the present invention is to provide an intelligent windshield or viewing screen, which is realized from an electro-optical glazing structure of the present invention. 
     These and other objects of the present invention will become apparent hereinafter and in the claims to Invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the Object of the Present Invention, the following Detailed Description of the Illustrative Embodiments of the Present Invention should be read in conjunction with the accompanying Drawings, wherein: 
         FIG. 1A  is a perspective view of a generalized embodiment of the intelligent electro-optical window system of the present invention, wherein the electro-optical glazing structure thereof is electrically switched under microcomputer-control to its totally-reflecting state of operation upon detecting a first set of preprogrammed electromagnetic conditions, whereby broad-band electromagnetic radiation is completely reflected off the electro-optical glazing structure thereof; 
         FIG. 1B  is a perspective view of the generalized embodiment of the intelligent electro-optical window system shown in  FIG. 1A , wherein the electro-optical glazing structure thereof is electrically switched under microcomputer-control to its transmission, state of operation upon detecting a second set of preprogrammed electromagnetic conditions, where broad-band electromagnetic radiation is transmitted through the electro-optical glazing structure thereof; 
         FIG. 2  is an exploded perspective view of a first illustrative embodiment of the electro-optical glazing structure of the present invention, showing an electrically-active π-phase retardation panel interposed between a pair of electrically-passive RHCP electromagnetic radiation reflecting panels, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 2A  is a schematic diagram of the RHCP electromagnetic radiation reflecting panel shown in  FIG. 2 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto; 
         FIG. 2B  is a schematic representation of the electromagnetic radiation reflection characteristics of the RHCP electromagnetic radiation reflecting panels of the glazing structure of  FIG. 2 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   RHCP       ;         
         FIG. 2C  is a schematic representation of a first embodiment of the it-phase retardation panel used in the construction of the glazing structure of  FIG. 2 , illustrating its operating characteristics in response to different glazing control voltages; 
         FIG. 2D  is a schematic representation of a second embodiment of the π-phase retardation panel used in the construction of the glazing structure of  FIG. 2 , illustrating its operating characteristics in response to different glazing control voltages; 
       FIG.  2 E 1  is a schematic diagram of a super broad-band π-phase retardation panel construction formed by interposing a twisted nematic, super-twisted nematic or cholesteric liquid crystal cell between a pair of electrically-passive broad-band π/2 phase retardation panels; 
       FIG.  2 E 2  is a schematic diagram of a broad-band π-phase retardation panel employed in the electrically-switchable super-broad band phase-retardation panel shown in FIG.  2 E 1 , made by laminating a plurality of narrow-band or broad-band π/2 layers, each realized using a material having a different birefringence and its π/2 phase-retardation characteristics centered about a different wavelength; 
       FIG.  2 E 3  is a graphical representation of the resulting π/2 phase, retardation characteristics provided by the cooperation of the phase retardatation characteristics of the individual narrow-band or broad-band π/2 layers used to construct the electrically-passive super-broad band π/2 phase-retardation panel shown in FIG.  2 E 2 ; 
         FIG. 3A  is a schematic diagram illustrating the operation of the glazing structure of  FIG. 2 , wherein the π-phase retardation panel of  FIG. 2C  is used and the control voltage provided thereto is selected (i.e., V=0, φ=π) so that the window panel is switched into its optically opaque or reflection state of operation; 
         FIG. 3B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 2 , where the π-phase retardation panel of  FIG. 2C  is used and the control voltage provided thereto is selected (i.e., V=1, 0) so that the window panel is switched into its the optically transparent (i.e. semi-clear) state of operation; 
         FIG. 4  is an exploded perspective view of a second illustrative embodiment of the intelligent electro-optical window of the present invention, comprising an electrically-active π-phase retardation panel interposed between a pair of electrically-passive LHCP, electromagnetic radiation reflecting panels, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 4A  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 4 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto; 
         FIG. 4B  is a schematic representation of the electromagnetic radiation reflection characteristics of the LHCP electromagnetic radiation reflecting panels of the window of  FIG. 4 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   LHCP       ;         
         FIG. 5A  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 4 , where the π-phase retardation panel of  FIG. 2D  is used and the control voltage provided thereto is selected (i.e., v=1, φ=π) so that the window panel is switched into its the opaque or reflection state of operation; 
         FIG. 5B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 5 , where the π-phase retardation panel of  FIG. 5D  is used and the control voltage provided thereto is selected (I.e., V=0, φ=0) so that the window panel is switched into its optically semi-transparent (i.e., semi-clear) state of operation; 
         FIG. 6  is an exploded perspective view of a third illustrative embodiment of the intelligent electro-optical window of the present invention, comprising an electrically-active π-phase retardation panel interposed between an electrically-passive RHCP electromagnetic radiation reflecting panel and an electrically-passive LHCP electromagnetic radiation reflecting panel, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 6A  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 6 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto; 
         FIG. 6B  is a schematic representation of the electromagnetic radiation reflection characteristics of the LHCP electromagnetic radiation reflecting panel of the window of  FIG. 6 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   RHCP       ;         
         FIG. 6C  is a schematic diagram of the RHCP electromagnetic radiation reflecting panel shown in  FIG. 6 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto; 
         FIG. 6D  is a schematic: representation of the electromagnetic radiation reflection characteristics of the RHCP electromagnetic radiation reflecting panel of the window of  FIG. 6 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   LHCP       ;         
         FIG. 7A  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 6 , where the π-phase retardation panel of  FIG. 2C  is used and the control voltage provided thereto is selected (i.e., v=0, φ=π) so that the window panel is switched into its the optically semi-transparent (i.e. semi-clear) state of operation; 
         FIG. 7B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 6 , where the π-phase retardation panel of  FIG. 2C  is used and the control voltage provided thereto is selected (i.e., v=0, φ=0) so that the window panel is switched into its optically opaque or reflection state of operation; 
         FIG. 8  is an exploded perspective view of a fourth illustrative embodiment of the intelligent electro-optical window of the present invention, comprising an electrically-active polarization rotation panel interposed between an electrically-passive linear polarizing. (LP 1 ) electromagnetic radiation reflecting panel and an electrically-passive LP 1  electromagnetic radiation reflecting panel, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 8A  is a schematic diagram of the LP 1  electromagnetic radiation reflecting panel shown in  FIG. 8 , and its response to both LP 1  and LP 2  electromagnetic radiation incident thereto; 
         FIG. 8B  is a schematic representation of the electromagnetic radiation reflection characteristics of the LP 1  electromagnetic radiation reflecting panel of the window of  FIG. 8 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   LP1       ;         
         FIG. 8C  is a schematic diagram of the LP 2  electromagnetic radiation reflecting panel shown in  FIG. 8 , and its response to both LP 1  and LP 2  electromagnetic radiation incident thereto; 
         FIG. 8D  is a schematic representation of the electromagnetic, radiation reflection characteristics of the LP 2  electromagnetic radiation reflecting panel of the window of  FIG. 8 , over its broadband range of operation, 
         Δ   ⁢           ⁢     λ   reflection   LP2       ;         
         FIG. 8E  is a schematic representation of an illustrative embodiment of the electro-optical glazing structure of  FIG. 8 , in which an electrically-switchable linear polarization direction rotating panel, realized using an electrically-controlled birefringence (ECB) cell, surface stablized ferroelectric liquid crystal. (SSFLC) cell, pi-cell, twisted nematic cell, super-twisted nematic cell, or cholesteric liquid crystal cell, is interposed between a pair of electrically-passive linear broad-band polarizing reflective panels realized using (1) broad-band CLC films with π/2 phase-retardation surfaces integrally formed therein and/or other types of reflective linear polarizers such as multi-layer interference linear polarizers; 
         FIG. 9A  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 8 , where the linear polarization direction rotating panel of  FIG. 8  is used and the control voltage provided thereto is selected (i.e., v=0, 90 degrees rotation) so that the window panel is switched into its transmission or semi-clear state of operation; 
         FIG. 9B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 9 , where the linear polarization direction rotating panel of  FIG. 8  is used and the control voltage provided thereto is selected (i.e., v=1, zero degrees rotation) so that the window panel is switched into its optically opaque state of, operation; 
         FIG. 10  is an exploded perspective view of a fifth illustrative embodiment of the intelligent electro-optical window of the present invention, comprising an electrically-passive π-phase retardation panel interposed between a first electrically-active LHCP electromagnetic radiation reflecting panel and a second electrically-active LHCP electromagnetic radiation reflecting panel, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 10A  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 10 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in the LHCP radiation reflecting state thereof; 
         FIG. 10B  is a schematic representation of the electromagnetic radiation reflection characteristics of the LHCP electromagnetic radiation reflecting panels of  FIG. 10 , over the broadband range of operation thereof 
         Δ   ⁢           ⁢     λ   reflection   LHCP       ,         
when operated in the LHCP radiation reflecting state thereof;
 
         FIG. 10C  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 10 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in the radiation transmission state thereof; 
         FIG. 10D  is a schematic representation of the electromagnetic transmission characteristics of the LHCP electromagnetic radiation reflecting panels of  FIG. 10 , over the broadband range of operation thereof 
         Δ   ⁢           ⁢     λ   tranmission   LHCP       ,         
when operated in the radiation transmission state thereof;
 
         FIG. 10E  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 10 , where the control voltages provided to both LHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically opaque state of operation; 
         FIG. 10F  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 10 , where the control voltages provided to both, LHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically transparent (i.e. clear) state of operation; 
         FIG. 11  is schematic cross-sectional diagram illustrating the construction of the first illustrative embodiment of the electrically-switchable, circularly polarizing CLC panels used in the electro-optical glazing structures of  FIGS. 10 ,  12  and  14 ; 
       FIG.  11 A 1  is a graphical representation of the reflection characteristics of the first embodiment of the electrically-switchable broad-band CLC panel of  FIG. 10 , measured prior to UV polymerization of the CLC material contained within the ITO coated substrate plates of the panel, using un-polarized light; 
       FIG.  11 A 2  is a graphical representation of the reflection characteristics of the first embodiment of the, electrically-switchable broad-band CLC panel of  FIG. 10 , measured subsequent to (curve (a)) and subsequent to ((curve ((b)) UV polymerization of the CLC material contained within the ITO coated substrate plates of the panel, using right-handed (curve (a)) and left handed (curve (b)) circularly polarized light; 
       FIG.  11 A 3  is a graphical representation of the reflection characteristics of the first embodiment of the electrically-switchable broad-band CLC panel of  FIG. 10 , measured during electrically inactive (no voltage applied) and electrically-active (voltage applied) states of operation using right-handed circularly polarized light; 
         FIG. 12  is an exploded perspective view of a sixth illustrative embodiment of the intelligent electro-optical window of the present invention, comprising an electrically-passive π-phase retardation panel interposed between a first electrically-active RHCP electromagnetic radiation reflecting panel and a second electrically-active RHCP electromagnetic radiation reflecting panel, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 12A  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 12 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in the RHCP radiation reflecting state thereof; 
         FIG. 12B  is a schematic representation of the electromagnetic radiation reflection characteristics of the RHCP electromagnetic radiation reflecting panels of  FIG. 12 , over the broadband range of operation thereof 
         Δ   ⁢           ⁢     λ   reflection   RHCP       ,         
when operated in the RHCP radiation reflecting state thereof;
 
         FIG. 12C  is a schematic diagram of the RHCP electromagnetic radiation reflecting panel shown in  FIG. 12 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in the radiation transmission state thereof; 
         FIG. 12D  is a schematic representation of the electromagnetic transmission characteristics of the RHCP electromagnetic radiation reflecting panels of  FIG. 12 , over the broadband range of operation thereof 
         Δ   ⁢           ⁢     λ   tranmission   RHCP       ,         
when operated in the radiation transmission state thereof;
 
         FIG. 13A  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 12 , where the control voltages provided to both RHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically opaque state of operation; 
         FIG. 13B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 12 , where the control voltages provided to both RHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically transparent (i.e. clear) state of operation; 
         FIG. 14  is an exploded perspective view of a seventh illustrative embodiment of the, intelligent electro-optical window of the present invention, showing an electrically-active LHCP electromagnetic radiation reflecting panel laminated to an electrically-active RHCP electromagnetic radiation reflecting panel, each made from CLC material having polarization-selective reflection characteristics over a broad-band region of the electromagnetic spectrum; 
         FIG. 14A  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 14 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in its LHCP radiation reflecting state; 
         FIG. 14B  is a schematic representation of the electromagnetic radiation reflection characteristics of the LHCP electromagnetic, radiation reflecting panel of  FIG. 14 , over its broadband range of operation 
         Δ   ⁢           ⁢     λ   reflection   LHCP       ,         
when operated in its LHCP radiation reflecting state;
 
         FIG. 14C  is a schematic diagram of the LHCP electromagnetic radiation reflecting panel shown in  FIG. 14 , and its response to both RHCP and LHCP electromagnetic radiation incident, thereto when operated in its radiation transmission state; 
         FIG. 14D  is a schematic representation of the electromagnetic radiation transmission characteristics of the LHCP electromagnetic radiation reflecting panel of  FIG. 14 , over its broadband range of operation 
         Δ   ⁢           ⁢     λ   tranmission   LHCP       ,         
when operated in its radiation transmission state;
 
         FIG. 14E  is a schematic diagram of the RHCP electromagnetic radiation reflecting panel shown in  FIG. 14 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in its RHCP radiation reflecting state; 
         FIG. 14F  is a schematic representation of the electromagnetic radiation reflection characteristics of the RHCP electromagnetic radiation reflecting panel of  FIG. 14 , over, its broadband range of operation 
         Δ   ⁢           ⁢     λ   reflection   RHCP       ,         
when operated in its RHCP radiation reflecting state;
 
         FIG. 14G  is a schematic diagram of the RHCP electromagnetic radiation reflecting panel shown in  FIG. 14 , and its response to both RHCP and LHCP electromagnetic radiation incident thereto when operated in its radiation transmission state; 
         FIG. 14H  is a schematic representation of the electromagnetic radiation transmission characteristics of the RHCP electromagnetic radiation reflecting panel of  FIG. 14 , over its broadband range of operation 
         Δ   ⁢           ⁢     λ   tranmission   RHCP       ,         
when operated in its radiation transmission state;
 
         FIG. 15A  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 14 , where the control voltages provided to both LHCP and RHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically opaque state of operation; 
         FIG. 15B  is a schematic diagram illustrating the operation of the intelligent electro-optical window of  FIG. 14 , where the control voltages provided to both RHCP electromagnetic radiation reflecting panels are selected so that the window panel is switched into its the optically transparent (i.e. clear) state of operation; 
         FIG. 16A  is a schematic diagram of a second, alternative embodiment of the electrically-switchable broad-band CLC panel of  FIG. 14 , showing a portion of un-polarized light being polarized in a first polarization state and reflected off CLC microflakes (i.e. CLC pigments) that are oriented in a parallel manner within electrically-active host nematic liquid crystal molecules homogeneously aligned between a pair of ITO coated plates, across which no control voltage is applied, while a second portion of the un-polarized light, is polarized in a second polarization state and transmitted through the oriented CLC microflakes; and 
         FIG. 16B  is a schematic diagram of the second embodiment of the electrically-switchable broad-band CLC panel of  FIG. 14 , showing the un-polarized light being transmitted between CLC microflakes that are oriented in a vertical manner within electrically-active host nematic liquid crystal molecules homotropically aligned between a pair of ITO coated plates, across which a control voltage is applied. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS OF THE PRESENT INVENTION 
     Referring now to the accompanying Drawings, six illustrative embodiments of the intelligent electro-optical window of the present invention will be described in great detail. In each of the figures, like structures and elements shall be indicated by like reference numerals. 
     In  FIGS. 1A and 1B , a generalized embodiment of the intelligent electro-optical glazing structure (i.e. window structure) of the present invention is shown installed within an environment (e.g. building or vehicle) having an interior space or volume adjacent the window structure. Typically, the interior space or volume functions as a form of human habitat, although there may be applications in which this is not the case. Preferably, the intelligent electro-optical window structure  1  cooperates with the heating/cooling system  2 A of a house, office building, factory or vehicle indicated by reference numeral  2 . In such preferred applications, the function of the electro-optical window structure will be to selectively control the flow of electromagnetic radiation through its electro-optical glazing structure and into the interior space, in order to minimize or reduce thermal loading upon the heating/cooling system of the environment. 
     As shown in  FIGS. 1A and 1B , the electro-optical glazing structure  1  comprises an electro-optical glazing panel  3  securely supported within a prefabricated window frame  4  which can be realized using virtually any suitable material such as, for example, plastic, metal, rubber, wood or composite material. Within the window frame, a number of system subcomponents are securely mounted, namely: a electromagnetic-radiation sensor  5  for sensing electromagnetic conditions in the outside environment; a rechargeable-type battery  6  for producing electrical power within the window frame; a electromagnetic-powered battery recharger  7  for recharging the rechargeable battery  6 ; a micro-controller (e.g. RISC-type micro-computer chip with onboard ROM, EPROM and RAM),  8  for controlling the battery recharger and glazing control signals as required by a radiation flow control program stored within the micro-computer chip; and electrical circuitry  9 , response to glazing control signals, for producing control voltages that are applied to the electrically-active elements of the electro-optical glazing structure  3  to electrically switch the same from one optical state to another optical state under microcontroller control. 
     As shown in  FIG. 1 , when a first set of preprogrammed electromagnetic conditions (e.g. a first prespecified band of electromagnetic radiation having power above a first prespecified power threshold) is detected by electromagnetic-radiation sensor, the electro-optical glazing structure  3  is electrically switched to its totally-reflecting state of operation under the control of preprogrammed microcontroller  8 . In this totally-reflecting state of operation, visible and electromagnetic, radiation is completely reflected off the, glazing structure over a broad band of spectral wavelengths (e.g. 400 to 750 nanometers). 
     As shown in  FIG. 1B , when a second set of preprogrammed electromagnetic conditions (e.g. a second prespecified band of electromagnetic radiation having power above a second prespecified power threshold) is detected by electromagnetic-radiation sensor, the electro-optical glazing structure  3  is electrically switched to its transmission state of operation under the control of preprogrammed microcontroller  8 . In this transmission state, visible and electromagnetic radiation is transmitted through the electro-optical glazing structure over a broad band of spectral wavelengths (e.g. 300 to 1000 nanometers). 
     While only two particular reflection/transmission states are illustrated in the above generalized embodiment, it is understood that virtually any set of reflection/transmission characteristics can be realized by the window structure of the present invention. In each such alternative embodiment, a particular set of conditions can be predefined to trigger a change in the optical state of the electro-optical glazing structure of the present invention. Then microcontroller is programmed to switch the optical state of the glazing structure upon detecting the corresponding condition. In alternative embodiments, the environmental condition or conditions which cause a switching operation, need not be related to electromagnetic radiation, but may be related to moisture, barometric pressure, temperature, or any other parameter prespecified within the programmed microcontroller  8 . 
     While in theory there exists an infinite number of embodiments of the electro-optical glazing structure of the present invention, six different embodiments of the electro-optical glazing structure will be described in detail below in order to illustrate the inventive features thereof. Notably, each electro-optical glazing structure of the present invention is realized using CLC material having polarization-selective reflection characteristics over a broad-band of operation (i.e. selectively reflecting and/or transmitting RHCP and LHCP wavelengths over the IR, visible and UV portions of the electromagnetic spectrum). An excellent tutorial and overview on the polarization-reflective properties of CLC materials and principles of polarization state conversion (i.e. linear-to-circular, circular-to-linear, linear-to-linear, circular-to-circular, unpolarized-to-linear, and unpolarized-to-circular) can be found in Applicant&#39;s U.S. Pat. No. 5,221,982, incorporated herein by reference in its entirety. 
     By virtue of such ultra broad-band operating characteristics of the electro-optical glazing material hereof, and the novel panel configurations disclosed herein, it is now possible to provide a level of electromagnetic radiation control hitherto unattainable by prior art smart window systems and methodologies. 
     First Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention 
     The first illustrative embodiment of the electro-optical Glazing structure hereof will be described with reference to  FIGS. 2 through 3B . 
     As shown in  FIG. 2 , the electro-optical glazing structure of the first illustrative embodiment  10  comprises: an electrically-active π-phase retardation panel  11  interposed between a pair of electrically-passive right-hand circularly polarized (RHCP) electromagnetic radiation reflecting panels  12 A and  12 B; respectively, for imparting a π-phase retardation to electromagnetic radiation transmitted therethrough in response to optical-state control voltages applied across the electrically-active π-phase retardation panel  11 ; and electrically conductive means  13  for applying optical-state control voltages to the electrically-active π-phase retardation panel  11 . Preferably, the electro-optical glazing structure of  FIG. 2  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A , and  1 B, and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     As illustrated In  FIGS. 2A and 2B , electromagnetic radiation having a RHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panels  12 A ( 12 B) is 100% reflected directly therefrom without absorption, while electromagnetic radiation, having either a LHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panels  12 A ( 12 B) is transmitted 100% directly therethrough, without absorption. Such electrically-passive, broad-band RHCP electromagnetic radiation reflecting panels can be made using, the fabrication methods disclosed in copending application Ser. No. 08/739,467 entitled “Circularly Polarizing Reflective Material Having Super Broad-Band Reflection And Transmission Characteristics And Method Of Fabricating And Using Same In Diverse Applications” by Le Li, Yingqiu Jiang and Sadeg M. Faris filed Oct. 29, 1996, and in application Ser. No. 08/550,022 entitled “Single Layer Reflective Super Broadband Circular Polarizer And Method Of Fabrication” by Sadeg M. Faris and Le Li, filed Oct. 30, 1995, both incorporated herein by reference in their entirety. Alternatively, narrow-band RHCP electromagnetic radiation reflecting panels  12 A ( 12 B) can be made using the fabrication methods disclosed in U.S. Pat. No. 5,221,982 to Faris, or using the techniques disclosed in U.S. Pat. No. 5,506,704 to Broer, et al. each being incorporated herein by reference in its entirety.
 
     There are a number of different ways in which to fabricate broad-band electromagnetic radiation reflecting panels  12 A ( 12 B) using the super broad-band, broad-band, narrow-band and spectrally-tunable CLC films taught in the above-cited references. 
     For example, broad-band circularly polarizing reflective panels  12 A ( 12 B) can be fabricated by producing sheets of such CLC film and then laminating the CLC film sheets onto a surface of glass or like substrate material physically associated with the electrically-switchable π-retardation panel  11  interposed between the circularly polarizing CLC panels, as shown in  FIGS. 2 ,  4 , and  6 , in particular. Notably, using the spectral-tuning techniques disclosed in detail in Applicants&#39; copending application Ser. No. 08/739,467, the CLC film hereof can be fabricated to have virtually any desired set of polarization reflection characteristics that would required by any particular application over a super broad-band of operation (e.g. from the UV region to the IR region of the electromagnetic spectrum). 
     Alternatively, sheets of super-broad-band, broad-band, narrow-band and/or spectrally-tuned CLC film can be produced as taught in the above references, and thereafter fragmented into microscopic sized CLC microflakes using film fragmentation techniques taught in U.S. Pat. No. 5,364,557. Then the CLC microflakes can be added to an optically transparent carrier fluid to produce a CLC ink or paint that can then be applied to the exterior surfaces of the glass substrates used to construct the electrically-switchable π retardation panel component of electro-optical glazing structures, of the type shown in  FIGS. 2 ,  4  and  6 , for example. The concentration of the CLC microflakes and the viscosity of the carrier medium (e.g. lacquer, polymer, etc.) should be selected to ensure that when the coating of the CLC ink or paint is applied to a substrate, the CLC microflakes will be distributed within the carrier medium so that incident light reflects from the resulting CLC coating in a non-specular manner. This will ensure that the resulting coating produces a “super-white” appearance in the eyes of on-viewers, providing a high measure of privacy, as well as aestethic value, highly desired in window applications. 
     In the illustrative embodiment of the glazing structure of  FIG. 2 , the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  12 A is designed to be substantially the same as characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  12 B. It is understood, however, that in alternative embodiments of the present invention, such reflection bandwidth characteristics may be specifically designed to partially overlap, or be separated from each other on the wavelength (i.e. frequency) domain in to provide desired reflection/transmission performance characteristics.
 
     In general, a π-cell (i.e. π-retardation panel) or an electrically controlled birefrigence (ECB) panel can be used to realize the electrically-switchable π-phase retardatation panel  11  employed in the circularly polarizing reflective glazing structures of  FIGS. 2 ,  4  and  6  hereof. Preferably, the techniques disclosed in U.S. Pat. No. 4,566,758 to Bos, incorporated herein by reference, are used to, fabricate such electrically-switchable π-phase retardatation panels  11 . For most applications, the bandwidth of prior art π-cells should be sufficient to provide glazing structures having operating characteristics over the visible portion of the electromagnetic spectrum. However, in some instances, it will be desirable to provide electro-optical glazing structures having super broad-band operation (i.e. from the IR region into the UV region of the spectrum). In such applications, it will be necessary to extend the π-phase retardatation characteristics of the electrically-switchable, π-phase retardatation panel beyond the visible band. The following technique may be used to construct electrically-active (switchable) π-retardation panels capable of super broad-band operation. 
     As shown in FIG.  2 E 1 , an electrically-switchable super broadband π-retardation panel can be constructed by interposing an electrically-active structure linear polarization direction rotating panel such as TN, or STN, or CLC cell, between a pair of electrically-passive super broad-band π/2 retardation panels (shifters). As shown in FIG.  2 E 2 , each super broad-band π/2-retardation panel is made by laminating, or depositing two or more broad-band or narrow-band π/2 retardation layers, each made from different material and having π/2 phase retardation characteristics centered about at different, wavelength, as schematically shown in FIG.  2 E 3 . These subcomponent broad-band or narrow-band π/2 retardation, layers can be made from liquid crystal material, birefringent polymer, and crystals. 
     The function of each electrically-passive super-broad-band π/2 retardation panel is to convert circularly polarized light into linearly polarized light which can be polarization direction rotated by the electrically switchable TN, or STN, or CLC cell sandwiched between the pair of super broad-band π/2 retardation layers. The function of the TN (twist nematic), or STN (super twist nematic), or CLC cell is to operate as an electrically-switchable optical rotator which rotates a linear polarization light by 90° when there is no electric field is applied across its ITO surfaces. If an electric field is applied, the, optical rotation power of the elements disappears. This control over the electric field allows the glazing structure to be switched from its total reflection state to its half reflection state, or vice versa. When the electrically-switchable polarization direction rotator is made from low-molecular weight (LMW) liquid crystal material having a chiral phase when no voltage is applied, then, its selective wavelength of the should be located outside the window operating spectrum region. By controlling the helix of the CLC molecules in the chiral phase, as well as the total thickness thereof, a 90° rotation of a linear polarization can be achieved. 
     In general, there are two different ways to configure electrically-switchable π retardation panel  11  in terms of external control voltages. In  FIGS. 2C and 2D , these configurations are specified. 
     In  FIG. 2C , the first embodiment of the π-phase retardation panel  11  is shown along with a specification of its various states of operation. As shown, when a non-zero voltage (e.g. 20 Volts) is applied across the phase retardation panel, 0-phase retardation is imparted to electromagnetic radiation transmitted therethrough. When a control voltage of zero volts is applied across the phase retardation panel, it imparts a π-phase retardation to electromagnetic radiation transmitted therethrough having, a wavelength within its operating band Δλ x  which is typically 300-1000 nanometers. 
     In  FIG. 2D , a second embodiment of the π-phase retardation panel is shown along with a specification of its states of operation. As shown, when a control voltage of zero volts is applied across this retardation panel, it imparts a O-phase shift to electromagnetic radiation having a wavelength within its operating band which is typically 350 nanometers, whereas π-phase retardation is imparted to such electromagnetic radiation when a non-zero voltage (e.g. 5-50 Volts) is applied thereacross. For wavelengths outside of the operating band, a phase shift other than π-radians is imparted to incident electromagnetic radiation when a non-zero voltage is applied. 
     Physically interfacing the subcomponent panels of the electro-optical glazing structure of  FIG. 2  can be achieved using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure of  FIG. 2  will now be described with reference to  FIGS. 3A and 3B , where the π-phase retardation panel of  FIG. 2C  is used in the construction of the glazing structure. 
     As shown in  FIG. 3A , the electro-optical glazing structure of  FIG. 2  is switched to its optically opaque state of operation by applying the appropriate control voltage thereacross (e.g. V=0 Volts). In this optical state, the electro-optical glazing structure reflects both LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident the window panel independent of the direction of propagation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in FIG.  3 A. Inasmuch as 100% of incident electromagnetic radiation is reflected from the surface of the electro-optical glazing structure, this glazing structure is “totally reflective” in this state of operation.
 
     As shown, in  FIG. 3B , the electro-optical glazing structure of  FIG. 2  is switched to its optically semi-transparent (i.e. semi-clear state) of operation by applying the appropriate control voltage thereacross (e.g. V=20 Volts). In this optical state, the electro-optical glazing structure reflects RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident the window panel independent of the direction of propagation, while transmitting LHCP electromagnetic radiation falling incident the window panel independent of the direction of electromagnetic radiation propagation. The physical mechanisms associated with such reflection and transmission processes are schematically illustrated in FIG.  3 A. Inasmuch as 50% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, while 50% of such electromagnetic radiation is reflected therefrom, this glazing structure can be said to “partially transmissive” in this state of operation.
 
Second Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention
 
     The second illustrative embodiment of the electro-optical glazing structure hereof will be described with reference to  FIGS. 4 through 5B . 
     As shown in  FIG. 4 , the electro-optical glazing structure of the second illustrative embodiment  14  comprises: an electrically-active (i.e. switchable) π-phase retardation panel  11  interposed between a pair of electrically-passive left-hand circularly polarizing (LHCP) electromagnetic radiation reflecting panels  15 A and  15 B, respectively; and electrically conductive means  16  for applying optical-state control voltages to the electrically-active π-phase retardation panel  11 . Preferably, the electro-optical glazing structure of  FIG. 4  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     As illustrated in  FIGS. 4A and 4B , electromagnetic radiation having a LHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panels  15 A,  155 B is reflected directly therefrom without absorption, while electromagnetic radiation having either a RHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the LHCP electromagnetic radiation reflecting panels is transmitted directly therethrough without absorption. Such electrically-passive, broad-band LHCP electromagnetic radiation reflecting panels can be made using the fabrication methods disclosed in: copending application Ser. No. 08/739,467 entitled “Circularly Polarizing Reflective Material Having Super Broad-Band Reflection And Transmission Characteristics And Method Of Fabricating And Using Same In Diverse Applications” by Le Li, Yingqiu Jiang and Sadeg M. Faris filed Oct. 29, 1996; and copending application Ser. No. 08/550,022 entitled “Single Layer Reflective Super Broadband Circular Polarizer And Method Of Fabrication” by Sadeg M. Faris and Le Li, filed Oct. 30, 1995, supra. In the preferred embodiment, the broad-band RHCP electromagnetic radiation reflecting panels  12 A ( 12 B) are fabricating by applying a coating of CLC-based ink (with suspended CLC flakes therein) onto a conventional glass panel, as taught in U.S. application Ser. No. 08/739,467, supra. Alternatively, narrow-band RHCP electromagnetic radiation reflecting panels can be made using the fabrication methods disclosed in U.S. Pat. No. 5,506,704 to Broer, et al, or the methods disclosed in U.S. Pat. No. 5,221,982 to Faris.
 
     Physically interfacing panels  11 ,  15 A and  15 B of the electro-optical glazing structure of  FIG. 4  can be achieved using conventional lamination techniques well known in the glazing art. 
     In the illustrative embodiment of the glazing structure of  FIG. 4 , characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  15 A is designed to be substantially the same as characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  15 B. It is understood, however, that in alternative embodiments of the present invention, such reflection characteristics may be specifically designed to partially overlap, or be separated from each other on the wavelength (i.e. frequency) domain in to provide desired reflection/transmission performance characteristics.
 
     The electrically-active π-retardation panel  11  can be constructed using any of the techniques described in detail above. 
     The operation of the glazing structure of  FIG. 4  will now be described with reference to  FIGS. 5A and 5B , where the π-phase retardation panel  11  of  FIG. 2C  is used in the construction of the glazing structure. 
     As shown in  FIG. 5A , the electro-optical glazing structure of  FIG. 4  is switched to its optically opaque state of operation by applying the appropriate control voltage thereacross (i.e. V=0 Volts). In this optical state, the electro-optical glazing structure  14  reflects both LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident the window panel, independent of its direction of propagation. As such, the operation, of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in FIG.  5 A. Inasmuch as 100% of incident electromagnetic radiation is reflected from the surface of the electro-optical glazing structure, this glazing structure is “totally reflective” in this state of operation.
 
     As shown in  FIG. 5B , the electro-optical glazing structure of  FIG. 4  is switched to its optically semi-transparent (i.e. semi-clear state) of operation by applying the appropriate control voltage thereacross (i.e. V=20 Volts). In this optical state, the electro-optical glazing structure  14  reflects LHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident the window panel, independent of its direction of propagation, while transmitting RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident the window panel, independent of the direction of electromagnetic radiation propagation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection and transmission processes are schematically illustrated in FIG.  5 A. Inasmuch as 50% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, while 50% of such electromagnetic radiation is reflected therefrom, this glazing structure is “partially transmissive” in this state of operation.
 
Third Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention
 
     The third illustrative embodiment of the electro-optical glazing structure, hereof will be described with reference to  FIGS. 6 through 7B . 
     As shown in  FIG. 6 , the electro-optical glazing structure of the third illustrative embodiment  17  comprises: an electrically-active π-phase retardation panel  11  interposed between an electrically-passive LHCP electromagnetic radiation reflecting panel  18 A and an electrically-passive RHCP electromagnetic radiation reflecting panel  18 B; and electrically conductive means  19  for applying optical-state control voltages to the electrically-active π-phase retardation panel  11 . Preferably, the electro-optical glazing structure of  FIG. 6  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     As illustrated in  FIGS. 6A and 6B , electromagnetic radiation having a LHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  18 A is reflected directly therefrom without absorption, while electromagnetic radiation having either a RHCP polarization state and/or a wavelength outside the characteristic reflection band 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption. In the preferred embodiment, the broad-band RHCP electromagnetic radiation reflecting panels  18 A are fabricating by applying a coating of CLC-based ink (with suspended CLC flakes therein) onto a conventional glass panel, as taught in U.S. application Ser. No. 08/739,67, and described hereinabove. Alternatively, narrow-band RHCP electromagnetic radiation reflecting panels  18 A can be made using, the fabrication methods disclosed in U.S. Pat. No. 5,221,982 to Faris, and while less preferred, using the methods disclosed in U.S. Pat. No. 5,506,704 to Broer, et al.
 
     As illustrated in  FIGS. 6C and 6D , electromagnetic radiation having a RHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  18 B is reflected directly therefrom without absorption, while electromagnetic radiation having either a LHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption. In the preferred embodiment, the broad-band RHCP electromagnetic radiation reflecting panels  18 B are fabricating by applying a coating of CLC-based ink (with suspended CLC flakes therein) onto a conventional glass panel, as taught in U.S. application Ser. No. 08/739,467, and described hereinabove. Alternatively, narrow-band RHCP electromagnetic radiation reflecting panels  18 B can be made using the fabrication methods disclosed in U.S. Pat. No. 5,221,982 to Faris, and using the less preferred techniques disclosed in U.S. Pat. No. 5,506,704 to Broer, et al.
 
     In the illustrative embodiment of the glazing structure of  FIG. 6 , characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  18 B is designed to be substantially the same as characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  18 A. It is understood, however, that in alternative embodiments of the present invention, such reflection bandwidth characteristics may be specifically designed to partially overlap, or be separated from each other on the wavelength (i.e. frequency) domain in to provide desired reflection/transmission performance characteristics.
 
     Electrically-active π retardation panel  11  can be realized using any of the construction techniques described in detail above. Physically interfacing panels  11 ,  18 A and  18 B of the electro-optical glazing structure of  FIG. 6  can be achieved using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure of  FIG. 6  will now be described with reference to  FIGS. 7A and 7B , where the π-phase retardation panel  11  of  FIG. 2C  is used in the construction of the glazing structure. 
     As shown in  FIG. 7A , the electro-optical glazing structure of  FIG. 6  is switched to its semi-optically transparent (i.e. clear) state of operation by applying the appropriate control voltage thereacross (i.e. V=0 Volts). In this optical state, the electro-optical glazing structure reflects LHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident on the LHCP electromagnetic radiation reflecting panel  18 A of the window panel, while transmitting RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident thereto and converting the same into LHCP electromagnetic radiation by the π-phase shifter as, it emanates from the RHCP electromagnetic radiation reflecting panel  18 B. In this optical state, the electro-optical glazing structure reflects RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident on the RHCP electromagnetic radiation reflecting panel  18 B of the window panel, while transmitting LHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident thereto and converting the same into RHCP electromagnetic radiation as it emanates from the LHCP electromagnetic radiation reflecting panel  18 A. As such, the operation of this particular electro-optical glazing structure is “assymmetrical”. The physical mechanisms associated with such reflection and transmission-reflection processes are schematically illustrated in  FIG. 7A  in great detail. Inasmuch as 50% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, while 50% of such electromagnetic radiation is reflected therefrom, this glazing structure is “partially transmissive” in this state of operation.
 
     As shown In  FIG. 7B , the electro-optical glazing structure of  FIG. 6  is switched to its optically opaque state of operation by applying the appropriate control voltage thereacross (i.e. V=20 Volts). In this optical state, the electro-optical glazing structure reflects LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident on the LHCP electromagnetic radiation reflecting panel of the window panel. In this optical state, the electro-optical glazing structure  17  also reflects RHCP and LHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident on the RHCP electromagnetic radiation reflecting panel  18 B of the window panel. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection and transmission-reflection processes are schematically illustrated in  FIG. 7B  in great detail. Inasmuch as 100% of incident electromagnetic radiation is reflected from the surface of the electro-optical glazing structure, this glazing structure is “totally reflective” in, this state of operation.
 
Fourth Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention
 
     The fourth illustrative embodiment of the electro-optical glazing structure hereof will be described, with reference to  FIGS. 8 through 9B . 
     As shown in  FIG. 8 , the electro-optical glazing structure of the fourth illustrative embodiment  19  comprises: an electrically-passive linear polarization direction rotating panel  19 C interposed between a first electrically-active linearly polarizing electromagnetic radiation reflecting panel  19 A having linearly polarization state LP 1 , and a second electrically-active LHCP electromagnetic radiation reflecting panel  19 C having linearly polarization state LP 2 , orthogonal to LP 1  or parallel; and electrically conductive means  19 D for applying optical-state control voltages to the electrically-active LHCP electromagnetic radiation reflecting panels  19 B and  19 C. Preferably, the electro-optical glazing structure of  FIG. 8  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     In  FIGS. 8A and 8B , the reflection characteristics of electrically-passive LP 1  electromagnetic radiation reflecting panel  19 B are illustrated. As shown, electromagnetic radiation having a LP 1  polarization state and a wavelength inside the characteristic, reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LP1         
 
of the LP 1  electromagnetic radiation reflecting panel is reflected directly therefrom without absorption, while electromagnetic radiation having either a LP 2  polarization, state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LP2         
 
of the LP 2 , electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption.
 
     In  FIGS. 8C and 8D , the reflection characteristics of electrically-active LP 2  electromagnetic radiation reflecting panel  19 C are illustrated. 
     As shown in  FIGS. 8C and 8D , electromagnetic radiation having a LP 1  polarization state and any wavelength within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   LP2         
 
is transmitted directly through the glazing panel without absorption, while electromagnetic radiation having either a LP 2  polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LP2         
 
of the LP 2  electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption.
 
     Electrically-passive LP 1  and LP 2  polarization reflective panels  19 A and  19 B can be made from super broad-band CLC film taught in Applicants” copending U.S. application Ser. No. 08/739,467 filed Oct. 29, 1996, and while less preferred, using the fabrication methods disclosed in U.S. Pat. No. 5,221,982 to Faris, and in U.S. Pat. No. 5,506,704 to Broer, et al. These applications disclose how to make circularly polarizing reflective CLC films. Such films can be converted into linearly polarizing CLC films using the novel phase-retardation imparting techniques taught in great detail in copending U.S. application Ser. No. 08/743,293 entitled “Liquid Crystal Film Structures With Phase-Retardation Surface Regions Formed Therein And Methods Of Fabricating The Same” by Sadeg Faris filed Nov. 4, 1996, incorporated herein by reference. The methods taught therein allows one to make an electrically passive broad-band linear polaring panel from a single layer of CLC film material, without laminating a π/2 phase-retardation panel to a layer of circularly polarizing CLC film. 
     An alternative method of making broad-band linearly polarizing reflective panels  19 A and  19 B is disclosed in U.S. Pat. No. 5,506,704 to Broer, et al. However, the fabrication techniques disclosed therein are less preferred than those taught in U.S. application Ser. No. 08/743,293, as the technique disclosed in U.S. Pat. No. 5,506,704 requires laminating a π/2 phase retardation panel to a circularly polarizing CLC film layer, which complicates manufacture and increases manufacturing costs. 
     The electronically-switchable linear polarization direction rotating panel  19 C employed in the electro-optical glazing structure of  FIG. 8  can be realized as an electrically-controlled birefrigence (ECB) cell, surface stabilized ferroelectric liquid crystal (SSFLC) cell, twisted nematic (TN) liquid crystal cell, super-twisted nematic (STN) liquid crystal cell, or CLC cell, whose operation is controlled by a control voltage well known in the art. To construct the linear polarization rotating cell  19 C, a layer of liquid crystal material is contained between a spaced apart pair of glass panels bearing layers of ITO on the interior surfaces thereof, and rubbed polyimide to provide liquid crystal alignment in a manner well known in the art. The ITO layers are used to create the necessary voltage across the layer of liquid crystal material and align the liquid crystal molecules, thereby preventing rotation of the polarization direction of linearly polarized light being transmitted therethrough during operation of the electro-optical glazing structure. 
     Physically interfacing panels  19 A,  19 B and  19 C of the electro-optical glazing structure of  FIG. 8  can be achieved using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure of  FIG. 8  will now be described with reference to  FIGS. 9A and 9B . 
     As shown in  FIG. 9A , the electro-optical glazing structure of  FIG. 8  is switched to its optically opaque state of operation by not applying a control voltage thereacross (i.e. V=0). In this optical state, the electro-optical glazing structure  19  reflects LP 1  electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LP1         
 
incident on the LP 1  electromagnetic radiation reflecting panel without adsorption, while transmitting LP 2  electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LP1         
 
incident thereto without adsorption. Also in this optical state, the electro-optical glazing structure  19  reflects LP 2  electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LP2         
 
incident on the LP 2  electromagnetic radiation reflecting panel without adsorption, while transmitting LP 1  electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LP2         
 
incident thereto without adsorption. As such, the operation of this particular electro-optical glazing structure is “assymmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in  FIG. 9A  in great detail. Inasmuch as 50% of incident electromagnetic radiation is reflected from the electro-optical glazing structure and 50% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, this glazing structure is “partially reflective” in this state of operation.
 
     As shown in  FIG. 9B , the electro-optical glazing structure of  FIG. 8  is switched to its optically transparent (i.e. clear) state of operation by applying the appropriate control voltage thereacross (i.e., V=1). In this optical state, the electro-optical glazing structure  19  reflects both LP 1  and LP 2  electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LP1         
 
and 
       Δ   ⁢           ⁢     λ   reflection   LP2         
 
incident on either electromagnetic radiation reflecting panel of the window panel without adsorption, independent of the direction of propagation of the incident electromagnetic radiation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such transmission processes are schematically illustrated in  FIG. 9B  in great detail. Inasmuch as 100% of incident electromagnetic radiation is transmitted through the electron-optical glazing structure, this glazing structure is “totally opaque” in this state of operation.
 
     The electro-optical glazing structure of  FIG. 8  can be readily adapted to exhibit “asymmetrical” reflection/transmission characteristics over its broad-band of operation by tuning the spectral transmission characteristics of both the CLC-based LP 1  and LP 2  electromagnetic radiation reflecting panels  19 A and  19 B of the illustrative embodiment so that the spectral reflection (and transmission) bandwidth characteristics thereof are either completely or partially overlapping or are separated on the wavelength (i.e. frequency) domain. Using such CLC-tuning techniques, it is possible to create an electro-optical glazing structure having the construction of  FIG. 8  which, when switched to its first optical state, is capable of totally reflecting electromagnetic radiation within a desired reflection band (e.g. within the ultraviolet and infrared bands) in a first direction defined with, respect to the panel, and when switched to its second optical state, totally transmitting electromagnetic radiation within such reflection band. 
     Fifth Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention 
     The fifth illustrative embodiment of the electro-optical glazing structure hereof will be described with reference to FIGS.  10  through  11 C 2 . 
     As shown in  FIG. 10 , the electro-optical glazing structure of the fifth illustrative embodiment  20  comprises: an electrically-passive π-phase retardation panel  21  interposed between a first electrically-active LHCP electromagnetic radiation reflecting panel  22 A and a second electrically-active LHCP electromagnetic radiation reflecting panel  22 B; and electrically conductive means  23  for applying optical-state control voltages to the electrically-active LHCP electromagnetic radiation reflecting panels  22 A and  22 B. Preferably, the electro-optical glazing structure of  FIG. 10  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     In  FIG. 10A , electrically-active LHCP electromagnetic radiation reflecting panel  22 A is shown operated in its electrically inactive state (i.e. when V=0). As shown in  FIG. 10C , electromagnetic radiation having a LHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel is reflected directly therefrom without absorption, while electromagnetic radiation having either a RHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption.
 
     In  FIG. 10B , the electrically-active LHCP electromagnetic radiation reflecting panel  22 B is shown operated in its electrically active state (i.e. when V=1). As shown in  FIG. 10D , electromagnetic radiation having a LHCP or RHCP polarization state and any wavelength within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   LHCP         
 
is transmitted directly through the glazing panel without absorption.
 
     The electrically-passive π-phase retardation panel  21  employed in the electro-optical glazing structure of  FIG. 10  can made from any material having a permanent birefringence which imparts to a π-phase retardation to electromagnetic radiation (within the operational band of the device). This panel can be fabricated from PVA, nematic liquid crystal, mica, etc. in a manner well known in the art. Methods for making such optical devices are disclose in U.S. Pat. No. 5,113,285 to Franklin, et al., incorporated herein by reference. 
     Electrically-switchable circularly polarizing reflective panels  22 A and  22 B can be fabricated using the construction techniques illustrated in FIGS.  11  through  11 A 3 . As shown in  FIG. 11 , each such panel generally comprises a pair of optically transparent plates  22 A 1  and  22 A 2  (e.g. made of glass, acrylic, etc.) spaced apart by a spacers  22 A 3  in a manner known in the art. In the illustrative embodiment, the spacing between the plates is about 20 microns, however, it is understood that such dimensions may vary from embodiment to embodiment of the invention. The internal surfaces of the plates are coated with a layer of ITO material  22 A 4  and  22 A to form optically transparent electrode surfaces. A polyimide coating is applied over the ITO layers, which is then rubbed to create director (i.e. alignment) surfaces for liquid crystal molecules to spontaneously order dance with the chiral phase, in a manner well-known in the art. Electrical leads are attached to the ITO layers. 
     Having formed a cell between the spaced apart plates  22 A 1  and  22 A 2 , a cholesteric liquid crystal (CLC) mixture  22 A 6  is prepared and then poured into the interior volume of the “cell” formed between the plates and spacers. In the illustrative embodiment set forth in  FIG. 10 , a “left-hand CLC formula” must be used to make the CLC mixture for the electrically switchable LCHP panels  22 A and  22 B. In the illustrative embodiment set forth in  FIG. 12 , a “right-hand CLC formula” must be used to make the CLC mixture for the electrically switchable RCHP panels  25 A and  25 B. In the illustrative embodiment set forth in  FIG. 14 , a “left-hand CLC formula” must be used to make the CLC mixture for the electrically switchable LHCP panel  28 A, and a “right-hand CLC formula” must be used to make the CLC mixture for the electrically switchable RHCP panel  28 B. These CLC formulas will be described in detail below. 
     According to the left-handed CLC formula, the following material components are measured and mixed together in a vessel, in the hereinafter specified “by weight” proportions, namely: 1 weight unit of liquid crystal polymerizable material having a left-handed cholesteric order (phase) (e.g. CC4039L from Wacker Chemical, Germany); 49.4 weight units of low-molecular weight nematic liquid crystal material (e.g. E7 from EMI, Inc. of Hawthorne, N.Y.); 0.026 weight units of UV photointiator (e.g. IG184 from Ciba Gigy); 0.30 weight units of a first left-handed chiral additive (e.g. R1011 from EMI, Inc.); and 0.42 weight units of a second left-handed chiral additive (e.g. CB15 from EMI, Inc.). 
     According to the right-handed CLC formula, the following material components are measured and mixed together in a vessel, in the hereinafter specified “by weight” proportions, namely: 1 weight unit of liquid crystal polymerizable material having a right-handed cholesteric order (phase) (e.g. CC4039R from Wacker Chemical, Germany); 49.4 weight units of low-molecular weight nematic liquid crystal material (e.g. E7 from EMI, Inc. Of Hawthorne, N.Y.); 0.026 weight units of UV photointiator (e.g. IG184 from Ciba-Gigy); 0.30 weight units of a first right-handed chiral additive (e.g. R1011 from EMI, Inc.); and 0.42 weight units of a second right-handed chiral additive (e.g. CB15 from EMI, Inc.). The spectral reflection characteristics for this particular right-handed CLC material (prior to UV polymerization) are shown in FIG.  11 A 1 . 
     After the appropriate CLC mixture has been made and poured into the cell region between the glass plates  22 A 1  and  22 A 2 , the panel structure is placed in a temperature-controlled curing cabinet containing a UV light source of controlled light intensity. The CLC panel structure is then cured within the cabinet. For the case of the above-described embodiment, using the above-described CLC mixture formulas, the CLC structure is cured for 12 hours while being maintained at 25° C. and exposed to UV light of 365 nm and power density 0.72 mW/cm 2 . 
     In FIG.  11 A 1 , the reflection characteristics of the RHCP CLC panel prior to UV polymerization are shown. In FIG.  11 A 2 , the reflection characteristics for the RHCP CLC panel after UV polymerization are shown when no voltage has been applied across the ITO coated plates. Notably, after UV polymerization, the reflection bandwidth of the CLC material has doubled. In FIG.  11 A 3 , the reflection characteristics for the RHCP CLC panel are shown when a voltage has been applied. Notably, the big reflection peak shown in FIG.  11 A 2  disappears due to the unwinding of the CLC helix of the CLC panel in the presence of the electric field created by the applied voltage. However, a weak peak is still observed in the reflection characteristics of this example due to the fact that the applied voltage had not been high sufficiently high enough intensity. 
     Having constructed the various subcomponents of the electro-optical glazing structure of  FIG. 10 , panels  21 ,  22 A and  22 B can then be physically interfaced as an integral unit using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure shown in  FIG. 10  will now be described with reference to  FIGS. 10E and 10F . 
     As shown in  FIG. 10E , the electro-optical glazing structure of FIG.  10  is switched to its optically opaque state of operation by not applying a control voltage thereacross (i.e. V=0). In this optical state, the electro-optical glazing structure  20  reflects LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident on either LHCP electromagnetic radiation reflecting panel without adsorption, independent of the direction of propagation thereof, as shown in FIG.  10 E. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in  FIG. 10E  in great detail. Inasmuch as 100% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, this glazing structure is “totally reflective” in this state of operation.
 
     As shown in  FIG. 10F , the electro-optical glazing structure of  FIG. 10  is switched to its optically transparent (i.e. clear) state of operation by applying the appropriate control voltage thereacross (i.e. V=1). In this optical state, the electro-optical glazing structure  20  transmits both LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident on either LHCP electromagnetic radiation reflecting panel of the window panel without adsorption, independent of the direction of propagation of the incident electromagnetic radiation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such transmission processes are schematically illustrated in  FIG. 10F  in great detail. Inasmuch as 100% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, this glazing structure is “totally transmissive” in this state of operation.
 
     The electro-optical glazing structure of  FIG. 10  can be readily adapted to exhibit “asymmetrical” reflection/transmission characteristics over its broad-band of operation by tuning the spectral transmission characteristics of both the CLC-based LHCP electromagnetic radiation reflecting panels  22 A and  22 B so that the spectral reflection (and transmission) bandwidth characteristics thereof are either completely or partially overlapping or are separated, on the wavelength (i.e. frequency) domain. Using such CLC-tuning techniques, it is possible to create an electro-optical glazing structure having the construction of  FIG. 10  which, when switched to its first optical state, is capable of totally reflecting electromagnetic radiation within a desired reflection band (e.g. within the ultraviolet and infrared bands) in a first direction defined with respect to the panel, and when switched to its second optical state, totally transmitting electromagnetic radiation within such reflection band. 
     Sixth Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention 
     The sixth illustrative embodiment of the electro-optical glazing structure hereof will be described with reference to  FIGS. 12 through 13B . 
     As shown in  FIG. 12 , the electro-optical glazing structure of the sixth illustrative embodiment  24  comprises: an electrically-passive π-phase retardation panel  21  interposed between a first electrically-active RHCP electromagnetic radiation reflecting panel  25 A and a second electrically-active RHCP electromagnetic radiation reflecting panel  25 B; and electrically conductive means  26  for applying optical-state control voltages to the electrically-active RHCP electromagnetic radiation reflecting panels  25 A and  25 B. Preferably, the electro-optical glazing structure of  FIG. 12  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     In  FIG. 12A , the electrically-active RHCP electromagnetic radiation reflecting panel  25 A ( 25 B) is shown being operated in its electrically inactive state (i.e. when V=0). As shown in  FIG. 12B , electromagnetic radiation having a RHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  25 A ( 25 B) is reflected directly therefrom without absorption, while electromagnetic radiation having either a LHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel is transmitted directly therethrough without absorption.
 
     In  FIG. 12C , the electrically-active RHCP electromagnetic radiation reflecting panel  25 A ( 25 B) is shown being operated in its electrically active state (i.e. when V=1). As shown in  FIG. 12D , electromagnetic radiation having a LHCP or RHCP polarization state and any wavelength within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   RHCP         
 
is transmitted directly through the electro-optical panel without absorption.
 
     The electrically-passive π-phase retardation panel  21  employed in the electro-optical glazing structure of  FIG. 12  can be realized in the manner described above in connection with the embodiment shown in  FIG. 12  above. The electrically-active, broad-band LHCP electromagnetic radiation reflecting panels  25 A and  25 B used in the glazing structure of  FIG. 10  can be made using the fabrication methods described above in connection with the embodiment shown in FIG.  10 . Physically interfacing panels  21 ,  25 A and  25 B of the electro-optical glazing structure of  FIG. 12  can be achieved using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure of  FIG. 12  will now be described with reference to  FIGS. 13A and 13B . 
     As shown in  FIG. 13A , the electro-optical glazing structure of  FIG. 12  is switched to its optically opaque state of operation by not applying a control voltage thereacross (e.g. V=0 Volts). In this optical state, the electro optical glazing structure  24  reflects LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident on the RHCP electromagnetic radiation reflecting panel  25 A ( 25 B) of the window panel without adsorption, independent of the direction of propagation of the incident electromagnetic radiation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in  FIG. 13A  in great detail. Inasmuch as 100% of incident electromagnetic radiation is reflected from the electro-optical glazing structure, this glazing structure is “totally reflective” in this state of operation.
 
     As shown in  FIG. 13B , the electro-optical glazing structure of  FIG. 12  is switched to its optically transparent (i.e. clear) state of operation by applying the appropriate control voltage thereacross (e.g. V=1 Volts). In this optical state, the electro-optical glazing structure  24  transmits both LHCP and RHCP electromagnetic radiation within 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident on either RHCP electromagnetic radiation reflecting panel  25 A (or  25 B) without adsorption, independent of the direction of propagation of the incident electromagnetic radiation. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such transmission processes are schematically illustrated in  FIG. 13B  in great detail. Inasmuch as 100% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, this glazing structure is “totally transmissive” in this state of operation.
 
     The electro-optical glazing structure of  FIG. 12  can be readily adapted to exhibit “asymmetrical” reflection/transmission characteristics over its broad-band of operation by tuning the spectral transmission characteristics of both the CLC-based RHCP electromagnetic radiation reflecting panels  25 A and  25 B so that the spectral reflection (and transmission) bandwidth characteristics thereof are either completely or partially overlapping or are separated on the wavelength (i.e. frequency) domain. Using CLC-tuning techniques, it is possible to create an electro-optical glazing structure having the construction of  FIG. 12  which, when switched to its first optical state, is capable of totally reflecting electromagnetic radiation within a desired reflection bandwidth (e.g. within the ultraviolet and infrared bands) in a direction defined with respect to the panel, and when switched to its second optical state, totally transmitting electromagnetic radiation within such reflection band. 
     Seventh Illustrative Embodiment of the Electro-Optical Glazing Structure of the Present Invention 
     The seventh illustrative embodiment of the electro-optical glazing structure hereof will be described with reference to  FIGS. 14 through 15B . 
     As shown in  FIG. 14 , the electro-optical glazing structure of the seventh illustrative embodiment  27  comprises: an electrically-active LHCP electromagnetic radiation reflecting panel  28 A; an electrically-active RHCP electromagnetic radiation reflecting panel  28 B laminated to panel  28 A; and electrically conductive means  29  for applying optical-state control voltages to the electrically-active LHCP and RHCP electromagnetic radiation reflecting panels  28 A and  28 B. Preferably, the electro-optical glazing structure of  FIG. 14  is mounted within a frame structure as described in connection with the generalized embodiment shown in  FIGS. 1A and 1B , and incorporates all of the power generation, electromagnetic radiation detection and micro-control mechanisms thereof. 
     In  FIG. 14A , the electrically-active LHCP electromagnetic radiation reflecting panel  28 A is shown being operated in its electrically inactive state (i.e. when V=0). As shown in  FIG. 14B , electromagnetic radiation having a LHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  28 A is reflected directly therefrom without absorption, while electromagnetic radiation having either a RHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
of the LHCP electromagnetic radiation reflecting panel  28 A is transmitted directly therethrough without absorption.
 
     In  FIG. 14C , the electrically-active LHCP electromagnetic radiation reflecting panel  28 B is shown being operated in its electrically active state (i.e. when V=1). As shown in  FIG. 14D , electromagnetic radiation having a LHCP or RHCP polarization state and any wavelength within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   LHCP         
 
is transmitted directly through the electro-optical panel  28 A without absorption.
 
     In  FIG. 14E , the electrically-active RHCP electromagnetic radiation reflecting panel  28 B is shown being operated in its electrically inactive state (i.e. when V=0). As shown in  FIG. 14F , electromagnetic radiation having a RHCP polarization state and a wavelength inside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  28 B is reflected directly therefrom without absorption, while electromagnetic radiation having either a LHCP polarization state and/or a wavelength outside the characteristic reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
of the RHCP electromagnetic radiation reflecting panel  28 B is transmitted directly therethrough without absorption.
 
     In  FIG. 14G , the electrically-active RHCP electromagnetic radiation reflecting panel  28 B is shown being operated in its electrically active state (i.e. when V=1). As shown in  FIG. 14H , electromagnetic radiation having a LHCP or RHCP polarization state and any wavelength within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   RHCP         
 
is transmitted directly through the electro-optical panel  28 B without absorption.
 
     The electrically-active, broad-band LHCP and RHCP electromagnetic radiation reflecting panels  28 A and  28 B used in the glazing structure of  FIG. 12  can be made using the fabrication methods described above in connection with the embodiment shown in FIG.  10 . Physically interfacing panels  28 A and  28 B of the electro-optical glazing structure of  FIG. 14  can be achieved using conventional lamination techniques well known in the glazing art. 
     The operation of the glazing structure of  FIG. 14  will now be described with reference to  FIGS. 15A and 15B . 
     As shown in  FIG. 15A , the electro-optical glazing structure of  FIG. 14  is switched to its optically opaque state of operation by not applying a control voltage thereacross (i.e. V=0). In this optical state, the electro-optical glazing structure  27  reflects LHCP and RHCP electromagnetic radiation within reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   LHCP         
 
incident on the LHCP electromagnetic radiation reflecting panel  28 A without adsorption, while reflecting LHCP and RHCP electromagnetic radiation within reflection bandwidth 
       Δ   ⁢           ⁢     λ   reflection   RHCP         
 
incident on the RHCP electromagnetic radiation reflecting panel  28 B without adsorption. As such, the operation of this particular electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such reflection processes are schematically illustrated in  FIG. 15A  in great detail. Inasmuch as 100% of incident electromagnetic radiation is reflected from the electro-optical glazing structure, this glazing structure is “totally reflective” in this state of operation.
 
     As shown in  FIG. 15B , the electro-optical glazing structure of  FIG. 14  is switched to its optically transparent (i.e. clear) state of operation by applying the appropriate control voltage thereacross (i.e. V=1). Assuming that the LHCP electromagnetic radiation reflecting panel  28 A and RHCP electromagnetic radiation reflecting panel  28 B each have the same characteristic transmission bandwidth (i.e. 
       Δ   ⁢           ⁢     λ   transmission   LHCP         
 
is the same as 
           Δ   ⁢           ⁢     λ   transmission   RHCP       )     ,       
 
then when switched in this optical state, the electro-optical glazing structure of  FIG. 14  transmits without adsorption, both LHCP and RHCP wavelengths within transmission bandwidth 
       Δ   ⁢           ⁢     λ   transmission   LHCP         
 
independent of whether such wavelengths fall incident on either the LHCP or RHCP electromagnetic radiation reflecting panel of the electro-optical glazing structure. As such, the operation of this particular embodiment of the electro-optical glazing structure is “symmetrical”. The physical mechanisms associated with such transmission processes are schematically illustrated in  FIG. 15B  in great detail. Inasmuch as 100% of incident electromagnetic radiation is transmitted through the electro-optical glazing structure, this glazing structure is “totally transmissive” in this state of operation.
 
     Notably, the electro-optical glazing structure of  FIG. 14  can be readily adapted to exhibit “asymmetrical” reflection/transmission characteristics over its broad-band of operation. Such characteristics can be imparted by tuning the spectral transmission characteristics of both the CLC-based RHCP and LHCP electromagnetic radiation reflecting panels  28 A and  28 B of the present invention so that the spectral characteristics thereof are either completely or partially overlapping or are separated on the wavelength (or frequency) domain. Using CLC-tuning techniques disclosed in application Ser. No. 08/739,467, it is possible to create an electro-optical glazing structure which, when switched to its first optical state, is capable of totally reflecting electromagnetic radiation within a desired reflection bandwidth (e.g. within the UV and IR bands) in a direction defined with respect to the panel, and when switched to its second optical state, totally transmitting electromagnetic radiation within the reflection band. 
     Having described the above illustrative embodiments of the present invention, a several modifications thereto and variations thereupon readily come to mind. 
     Alternatively, the electrically-active LHCP and RHCP reflecting panels  28 A and  28 B panels in the glazing structure of  FIG. 14  can be realized using the novel electro-optical construction schematically illustrated in  FIGS. 16A and 16B . 
     As shown in  FIGS. 16A and 16B , the physical construction of this alternative embodiment of the electrically-switchable broad-band CLC panels  28 A ( 28 B) is very similar to that of the panels described above in connection with FIGS.  11  through  11 A 3 . However, in this alternative embodiment shown in  FIGS. 16A and 16B , the broad-band (or super broad-band) CLC material contained between glass plates thereof is radically different from that contained with the panel illustrated in FIGS.  11  through  11 A 3 , as will be explained below. 
     The novel material contained between the plates of this novel electrically-switchable super-broadband CLC (BBCLC) polarizer is made from polymerizable liquid crystal blends in cholesteric order. According to this aspect of the present invention, “functional pigment suspended liquid crystal” (FPSLC) material is created by mixing (i) broad-band CLC pigments (e.g. CLC microflakes taught in application Ser. No. 08/739,467) into (ii) an electrically-active (i.e. electrically-responsive) carrier fluid such as a low-molecular weight (LMW) nematic liquid crystal fluid (e.g. E7 and E44) which is commercially available from EMI of Hawthorne, N.Y. As will be explained in greater detail hereinafter, the micro-sized functional pigments of this particular embodiment have unique optical properties that can be exploited in various applications including electro-optical glazing structures. In the illustrative embodiment, the functional pigments are realized using BBCLC microflakes having a size in the range of about 20-100 microns. When making the LHCP panel  28 A, left-handed BBCLC microflakes should be used, whereas when making the RHCP panel  28 B, right-handed BBCLC microflakes should be used. The mass density of the CLC microflakes should be substantially equal to the mass density of the LMW carrier liquid fluid. Also the refractive index of the CLC microflakes should be matched closely to the refractive index of the carrier fluid. 
     Once prepared, the FPSLC mixture is poured into a cell constructed from a pair of spaced apart ITO-coated glass or plastic plates. To achieve the required liquid crystal alignment, the ITO layers are coated with rubbed polyimide in a manner well known in the art. The ITO layers are also provided with electrical leads so that an external field can be impressed across the ITO coated glass plates. As will be illustrated greater detail below, this makes the FPSLC material between the plates electrically-active or switchable between its electro-optical states of operation. Notably, when making such electrically-switchable plates, there is no UV polymerization step, as in the above-described fabrication methods. 
     After the filling operation, the CLC pigments are uniformly distributed inside the cell in order to cover the entire cell area. The cell thickness is designed to be larger than the pigment dimension. It is assumed that the liquid crystal molecules are spontaneously aligned in homogeneous state due to the surface coating. The homogeneous alignment of the host LC molecules forces the CLC pigments to align parallel to the cell surface, as shown in FIG.  16 A. The switching or reorientation of the host liquid crystal molecules by an applied electric field forces the suspended CLC pigments to be reoriented accordingly, as shown in FIG.  16 B. For purposes of convention, it will be helpful to designate state “A” of the host liquid crystal as the state when there is no electrical field is applied, as illustrated in FIG.  16 A. Accordingly, the CLC pigments are assigned to be in state “A clc ”. Once a strong enough field, e.g., an electric field, is applied, the host liquid crystal molecules are reoriented to state “B” as shown in FIG.  16 B. Accordingly, the CLC pigments are reoriented from state “A clc ” to state “B clc ”. Since the BBCLC pigments in the host liquid crystal preserve the same polarization property, then its parallel orientation should exhibit a polarizing state for an incoming light onto the cell surface. If the CLC microflakes are vertically aligned due to the reorientation of the host liquid crystal molecules under an applied field, then the cell loses the capability to polarize light and becomes transparent or quasi-transparent, i.e. provided that the thickness of the CLC microflakes is much smaller than the aerial dimension of the electro-optical cell. 
     The electrically-switchable circularly polarizing panels of the type shown in  FIGS. 16A and 16B  can be realized in a variety of configurations. These alternative configurations will be described below. 
     Parallel-to-Vertical Configuration (Case I) 
     In this configuration, the cell is constructed so that the host nematic liquid crystal adopts a spontaneous alignment in homogeneous state. The ITO substrate is coated with a polyimide favorable for such an alignment followed by a mechanical rubbing. If the host liquid crystal has a positive dielectric anisotropy, it can be vertically reoriented into a homeotropic state by an electric field (E-field). In this case, state “A” of the host LC refers to homogeneous, and state “B” to homeotropic; while state “A clc ” and “B clc ” of the CLC pigments refers to parallel and perpendicular to the cell surface, respectively, as schematically shown in FIG.  16 A. In this way, the panel can be switched from polarizing reflection to transparent or quasi-transparent state. Varying the strength of the E-field can change the final reflectivity of the panel. It should be pointed out that rubbed polyimide is not the only choice for surface treatment. Other techniques are also applicable, such as oblique deposition of SiOx, UV alignable layers, etc. 
     Parallel-to-Vertical Configuration (Case II) 
     In this configuration the cell is constructed so that the host low molecular weight (LMW) cholesteric liquid crystal adopts a spontaneous alignment in the planar state. The pitch of the LMW CLC can be tuned either inside or outside of the CLC pigment reflection spectral region. The ITO substrate is coated with a rubbed polyimide favorable for planar alignment. If the host liquid crystal in cholesteric order has a positive dielectric anisotropy, it can be reoriented vertically into a homeotropic state by an electric field (E-field). In this case, state “A” of the host LC refers to planar, and state “B” to homeotropic; while state A clc ” and “B clc ” of the CLC pigments refers to parallel and perpendicular to the cell surface, respectively. Thus the panel can be switched from polarizing reflection to transparent state. Varying the strength of the E-field can change the final reflectivity of the panel. It should be pointed out that rubbed polyimide is not the only choice for surface treatment. Other techniques are applicable, such as oblique deposition of SiOx, UV alignable layers, etc. In some cases, no alignment layer is required. 
     Vertical-to-Parallel Configuration (Case I) 
     In this configuration, the cell is constructed so that the host nematic liquid crystal adopts a spontaneous alignment in homeotropic state. The ITO substrate is coated with an alignment agent favorable for such an alignment. No mechanical rubbing is necessary. If the host liquid crystal has a negative dielectric anisotropy, it can be reoriented into a homogeneous state by an electric field (E-field). In this case, state “A” of the host LC refers to homeotropic, and state “B” to homogeneous; while state “A clc ” and “B clc ” of the CLC pigments refer to perpendicular and parallel to the cell surface, respectively. Thus the panel can be switched from transparent to polarizing reflection state. Varying the strength of the E-field can change the final reflectivity of the panel. 
     Vertical-to-Parallel Configuration (Case II) 
     In this configuration, the cell is constructed so that the host low molecular weight (LMW) cholesteric liquid crystal adopts a spontaneous alignment in homeotropic state. The pitch of the LMW CLC can be tuned either inside or outside of the CLC pigment reflection spectral region. The ITO substrate is coated with an alignment agent favorable for homeotropic alignment. If the host liquid crystal in cholesteric order has a negative dielectric anisotropy, it can be reoriented into a planar state by an electric field (E-field). In this case, state “A” of the host LC refers to homeotropic, and state “B” to planar; while state “A clc ” and “B clc ” of the CLC pigments refers to perpendicular and parallel to the cell surface, respectively. Thus the panel can be switched from transparent to polarizing reflection state. Varying the strength of the E-field can change the final reflectivity of the panel. 
     FPSLC with Polymer Network 
     In this preferred configuration, the cell is constructed so that the host low molecular weight (LMW) liquid crystal in cholesteric order contains a small amount of polymer network which is formed by UV polymerizing a polymer material mixed inside the LMW LC in absence of any field. The purpose of introducing the polymer network is to realize a bistable state, i.e., weak scattering state and high reflection state of the panel and, possibly, improving the reflectivity. The polymer network helps to better confine CLC flakes in a preferred orientation, for example, a parallel orientation. The host liquid crystal can adopt either an ECB or TN or STN or cholesteric order. The ITO substrate is coated with a polyimide favorable for a homogeneous alignment. If the host liquid crystal in cholesteric order has a positive dielectric anisotropy, it can be reoriented from planar to homeotropic state by an electric field (E-field). In this case, state “A” of the host LC refers to homogeneous, and state “B” to homeotropic; while state “A clc ” and “B clc ” of the CLC pigments refers to parallel and perpendicular to the cell surface, respectively. Thus the panel can be switched from polarizing reflection to semi-or total transparent state. Varying the strength of the E-field can change the final reflectivity of the panel. Another important feature of this polymer stabilized FPSLC configuration is that a reflection and scattering mixed mode can be realized by properly controlling polymer density and applied voltage, similar to the conventional polymer stabilized cholesteric texture (PSCT). 
     FPSLC with Surface Stabilization Function 
     In this preferred configuration, the cell is constructed so that the host low molecular weight (LMW) liquid crystal in cholesteric order is surface stabilized which exhibits also a bistable state, i.e., weak scattering state and relatively high reflective state. This texture helps to better confine CLC flakes in a preferred orientation, for example, a parallel orientation. The ITO substrate is coated with a polyimide favorable for a homogeneous alignment. If the host liquid crystal in cholesteric order has a positive dielectric anisotropy, it can be reoriented from planar to homeotropic state by an electric field (E-field). In this case, state “A” of the host LC refers to homogeneous, and state “B” to homeotropic; while state “A clc ” and “B clc ” of the CLC pigments refers to parallel and perpendicular to the cell surface, respectively. Thus the panel can be switched from polarizing reflection to semi-or total transparent state. Varying the strength of the E-field can change the final reflectivity of the panel. Another important feature of this surface-stabilized FPSLC configuration is that a reflection and scattering mixed mode can be realized by properly controlling polymer density and applied voltage, similar to the conventional polymer stabilized cholesteric texture (PSCT). 
     Each of the cell configurations described above can be used to build a switchable (super) broadband FPSLC panel which is electrically switchable from reflection state to transparent state, or vice versa. The reflected light is polarized and can cover a broad spectral bandpass, such as the entire visible region. Ideally, in a perfect reflection state, 50% of the incident light is reflected into one polarization state and another 50% is transmitted in other polarization state. However, when switched into the total transmission mode, the panel passes 100% of the incident light. Varying the strength of the E-field can change the final reflectivity between 0% and 50% (equivalently, the transmittance can be varied between 50% to 100%). 
     The electrically-switchable FPSLC-based structures described above can be used to realize the electrically-switchable circularly polarizing panels employed in the systems shown in  FIGS. 10 and 12  hereof. In such electro-optical glazing structures, the particular compositions used to created the FPSLC material will vary in order to provide the required polarization reflective functions. For example, when making broad-band LHCP panels  22 A and  22 B, left-handed BBCLC microflakes should be added to the LMW liquid crystal carrier fluid of the FPSLC mixture thereof. When making broad-band RHCP panels  25 A and  25 B, right-handed BBCLC microflakes should be added to the LMW liquid crystal carrier fluid of the FPSLC mixture thereof. When making RHCP panels  25 A and  25 B having spectrally-tuned reflection characteristics, right-handed BBCLC microflakes with narrow-band reflection characteristics should be added to the LMW liquid crystal carrier fluid of the FPSLC mixture thereof. For example, five color CLC microflakes (i.e. pigments) can be added into the LMW liquid crystal carrier fluid in order to cover the visible band. It is understood, various combinations of left and right handed CLC microflakes (having super broad-band, broad-band and/or narrow-band polarization reflection characteristics) can be added to the LMW liquid crystal carrier fluid in order to produce electrically-switchable circularly polarizing glazing structures having diverse polarization reflection characteristics adapted to meet any application imaginable. 
     Having described such alternative embodiments of the present invention, further modifications thereto readily come to mind. 
     For example, the electro-optical glazing structures described above can be stacked and laminated together, in virtually any number or ordering, so as form composite electro-optical glazing structures having more than two optical states (e.g. four or more). Such electro-optical glazing structures can be used to construct sophisticated window systems capable of providing complex levels of solar and/or visible radiation control. 
     Electrically controlled CLC-based smart windows of the present invention can be used in homes, schools, offices, factories, as well as in automobiles and airplanes to provide privacy, brightness control, and reduce thermal loading on heating and cooling systems employed therein. 
     The electro-optical glazings of the present invention can be used to make intelligent sunglasses and sun visors for use in a variety of applications. In such embodiments of the present invention, the electro-optical glazing of the present invention is realized in the form of a pair of lenses which are mounted within a frame supportable upon the head of its user, as in conventional eyeglasses or sun-visors. The programmed microcontroller, battery, electromagnetic detector, battery recharging circuitry and optical state switching circuitry embodied within the window frame shown in  FIGS. 1A and 12B  can be reduced in size and embodied within the ultra-compact sunglasses frame of this illustrative embodiment of the present invention. 
     In yet another alternative embodiment of the present invention, the electro-optical glazing structures of the present invention can be mounted before each LCD viewing panel within the shutter-type stereoscopic 3-D viewing glasses disclosed in copending application Ser. No. 08/648,215 filed on May 15, 1996, incorporated herein by reference in its entirety. Advantageously, the application of the present invention thereto would provide stereoscopic 3-D viewing glasses having several additional modes of operation, wherein the user could simply control electromagnetic radiation in either a manual or automatic manner during stereoscopic 3-D viewing or monoscopic 2-D viewing of displayed images (i.e. virtual world viewing), or stereoscopic viewing of real world objects while walking, bicycling, jogging, sailing, or just lounging about in the rays of the Sun. 
     The electro-optical glazings of the present invention can be used in automotive vehicles, maritime vessels, aircrafts and spacecrafts. 
     The modifications described above are merely exemplary. It is understood that other modifications to the illustrative embodiments will readily occur to persons with ordinary skill in the art. All such modifications and variations are deemed to be within the scope and spirit of the present invention as defined by the accompanying Claims to Invention.