WO2001022867A1

WO2001022867A1 - Inspection device containing a switchable holographic optical element

Info

Publication number: WO2001022867A1
Application number: PCT/US2000/026860
Authority: WO
Inventors: Milan M. Popovich
Original assignee: DigiLens Inc
Current assignee: DigiLens Inc
Priority date: 1999-09-29
Filing date: 2000-09-29
Publication date: 2001-04-05
Anticipated expiration: 2002-03-29
Also published as: AU7737000A

Abstract

An inspection device (10) is disclosed that employs a switchable holographic optical element (SHOE) (28). In one embodiment, the inspection device, or a portion thereof, may include a tube (24) extending between first and second ends, a SHOE (28), and a conductor (38) coupled to the SHOE. The SHOE is switchable between active and inactive states. When in the active state, the SHOE diffracts a bandwidth light incident thereon. When in the inactive state, the SHOE transmits a bandwidth light incident thereon without substantial alteration. The conductor, a portion of which is contained within the tube between the first and second ends thereof, transmits control signals or voltages to the SHOE.

Description

INSPECTION DEVICE CONTAINING A SWITCHABLE HOLOGRAPHIC OPTICAL ELEMENT

RELATED APPLICATIONS

5 This application claims priority to US Provisional Application Serial No.

60/156,773 filed September 29, 1999.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to devices for inspecting hard to access 10 areas. More particularly, the present invention relates to an inspection device employing an electrically switchable holographic optical element (SHOE) system. The present invention may find application in a wide variety of matters. However, the present invention will be described with reference to use with an endoscope, it being understood that the present invention should not be limited thereto.

15 Background

Endoscopes, or other instruments for viewing the interior of spaces not accessible to direct examination, are well known in the art. In one class of endoscopes within the prior art, an image is formed by an objective optical system of conventional optical elements positioned at a distal end of a tubular member and is transferred through the

20 tubular member to an image forming device at the proximal end of the tube. The image forming device may include an optical eyepiece for direct viewing, or an electronic imaging device and associated circuitry for providing a visible image on an electronic display screen. In this class of prior art endoscopes, the image formed at the distal tip may be transferred by a fiber optic bundle to the image forming device at the proximal

25 end of the endoscope. Using the fiber optic bundle enables flexibility of the endoscope, which has particular value in medical applications.

Still another class of prior art endoscopes employs a solid state imaging element, typically a charge-coupled device (CCD) positioned adjacent an optical objective system at the distal end and in optical communication therewith, so that image signals may be formed at the distal tip of the endoscope. In this prior art embodiment, only wire conductors are needed to transfer the image signals from the distal end of the endoscope to an electronic imaging device at the proximal end. This prior art endoscope, like the embodiment employing the fiber optic bundle described above, can be made relatively flexible.

Prior art endoscopes also teach the transmission of illumination light from a light source located at the proximal end of the endoscope to its distal end via flexible fiber optic bundle contained within flexible tubing. A dispersing conventional optical element positioned at the tip of the fiber optical bundle, enables the light emitted by the fiber optical bundle to diverge and illuminate a broader field of view.

SUMMARY OF THE INVENTION

The present invention relates to an inspection device employing a switchable holographic optical element (SHOE). In one embodiment, the inspection device, or a portion thereof, may include a tube extending between first and second ends, a first SHOE, and a first conductor coupled to the first SHOE. The first SHOE is switchable between active and inactive states. When in the active state, the first SHOE diffracts first bandwidth light incident thereon. When in the inactive state, the first SHOE transmits first bandwidth light incident thereon without substantial alteration. The first conductor, a portion of which is contained within the tube between the fist and second ends thereof, transmits control signals or a controllable voltage for switching the first SHOE between the active and inactive states.

The present invention may also include an imaging device comprising an array of light detectors such as a CCD, coupled to a second conductor. The imaging device may generate signals in response to receiving light transmitted or diffracted by the first SHOE. The signals generated by the imaging device maybe transferred over the second conductor to, for example, processing circuitry for subsequent display on a video monitor. A portion of the second conductor, like the first conductor, extends within the tube between the first and second ends thereof. In one embodiment, each of the tube, first conductor, and second conductor, is flexible. In another embodiment, the present invention may include second and third SHOEs in addition to the first SHOE. Each of these second and third SHOEs, like the first SHOE, is switchable between active and inactive states. In the active state, the second SHOE diffracts second bandwidth light incident thereon. In the active state, the third SHOE diffracts a third bandwidth light incident thereon. In the inactive state, the second and third SHOEs transmit second and third bandwidth light incident thereon respectively, without substantial alteration. Both of the first and second SHOEs may be positioned adjacent to the first SHOE and in optical communication therewith. The first SHOE, when active or inactive, transmits a second and third bandwidth light without substantial alteration. The second SHOE, when active or inactive, transmits first and third bandwidth light without substantial alteration. The third SHOE, when active or inactive, transmits first and second bandwidth light without substantial alteration. The first, second and third bandwidth lights are different from each other and represent, in one embodiment, the red, green and blue bandwidths, respectively, of visible light.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and it's numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the figures designates a like or similar element.

Figure 1 is a schematic diagram of an endoscopic system including a cross sectional view of a portion of an endoscope employing one embodiment of the present invention;

Figure 2 is a schematic diagram of an endoscopic system including a cross sectional view of a portion of an endoscopic employing a second embodiment of the present invention;

Figure 3A is a schematic diagram of an endoscopic system including a cross sectional view of a portion of an endoscope employing a third embodiment of the present invention; Figure 3B is an end view of the endoscope of Figure 3 A without the electrically switchable holographic optical system;

Figure 4 is a schematic diagram of an endoscopic system including a cross sectional view of a portion of an endoscope employing a fourth embodiment of the present invention;

Figure 5 is a block diagram of the electrically switchable holographic optical system coupled to the control and processing circuit of Figures 1-4;

Figure 6a shows in cross section one embodiment of a switchable holographic optical element for use in the electrically switchable holographic optical system of Figure 5;

Figure 6b shows in cross section another embodiment of a switchable holographic optical element for use in the electrically switchable holographic optical system of Figure

5;

Figures 7a-7c illustrate operational aspects of a first embodiment of the electrically switchable holographic optical system of Figure 5;

Figures 8a-8c illustrate operational aspects of a second embodiment of the electrically switchable holographic optical system of Figure 5;

Figure 9 illustrates operational aspects of a third embodiment of the electrically switchable holographic optical system of Figure 5;

Figure 10 illustrates operational aspects of a fourth embodiment of the electrically switchable holographic optical system of Figure 5:

Figure 11 illustrates operational aspects of a fifth embodiment of the electrically switchable holographic optical system of Figure 5, and;

Figure 12 illustrates operational aspects of a sixth embodiment of the electrically switchable holographic optical system of Figure 5.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail, it should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention relates to an inspection device employing switchable holographic optical elements. The present invention will be described with reference to an endoscope, it being understood the present invention should not be limited thereto. Figure 1 shows an endoscopic system 10 including an endoscope 12 shown in cross section. For ease of description, endoscope 12 is partially shown such that Figure 1 shows only distal and proximal portions 14 and 16, respectively. Endoscopic system 10 further includes control and processing circuit 18, video display 20, and illumination system 22. The endoscope 12 includes a flexible tube 24, an imaging device 26, and an electrically switchable holographic optical system 28. The imaging device 26 may take form in an array of photodetector elements (preferably a CCD array) which is in optical communication with the electrically switchable holographic optical system 28. More particularly, imaging device 26 receives light transmitted through or diffracted by electrically switchable holographic optical system 28, as will be more fully described below.

Tube 24 is preferably flexible. However, the present invention should not be limited thereto. Rather, tube 24 may take form in a rigid structure. Tube 24 includes an outer wall 30 which surrounds and inner cylindrical passage. Annular core section 32 and conductors 34 through 38 extend within in the passage of tube 24. Annular core section 32 and conductors 34 through 38 may be rigid. However, in the preferred mode, annular core section 32 and conductors 34 through 38 are flexible. Annular core section 32 acts as a light guide for transmitting light from the illumination system 22. Conductors 34 through 38 function to transmit signals and or power between control and processing circuit 18, imaging device 26, and electrically switchable holographic optical system 28.

As can be seen from Figure 1, conductors 34 and 36 couple imaging device 26 to control and processing circuit 18. One or more conductors 38 couple electrically switchable holographic optical system 28 to control and processing circuit 18. One or more conductors 34 transmit image signals generated by imaging device 26 in response to receiving and converting light transmitted or diffracted by electrical switchable holographic optical system 28. One or more conductors 36 provide timing signals and/or power to imaging device 26. One or more conductors 38 provides control signals and/or switching voltage to electrically switchable holographic optical system 28 as will be more fully described below. Alternatively, a switching voltage and/or control signals for optical system 28 may be provided by imaging device 26. For example, imaging device 26 may include a circuit which generates control signals for the optical system 28. The control signals generated by the imaging device 26 may be triggered by imaging device timing signals transmitted over one or more of the conductors 36.

Illumination system 22 includes a light source 40 and, optionally, a condensing lens 42. Illumination system 22 is positioned adjacent a proximal end of endoscope 12. Light source 40 generates light which is received by condensing lens 42 (if present). Condensing lens 42 focuses or concentrates the received light for input to annular core section 32. Annular core section 32 will often be described herein as light guide 32. Light source 40 may include a light emitting device such as a white light source, light emitting diodes (LEDs), or one or more lasers. Further, light source 40 may include a switchable filter formed of one or more switcahble holographic optical elements described in copending application serial No. 09/351,412 entitled Projection System Based On Reconfigurable Holographic Optics filed July 9, 1999 and incorporated herein by reference in its entirety. In one embodiment, light source 40 includes a white light source (not shown) and the switchable filter (not shown) mentioned above. In this embodiment, white light output of the white light source is sequentially and cyclically filtered by the switchable filter into, for example, red, green, and blue bandwidth light prior to input to the condensing lens 42 or light guide 32. In this embodiment, only red, green, or blue bandwidth light is input to condensing lens 42 or light guide at any given moment. In another embodiment, light emittting device may produce or the switchable filter mentioned above may filter light from the emmitting device to produce near

UV blue light (typically, incoherent or laser light in the range 400 to 450 nm). Other wavelengths are contemplated. Near UV/blue light is useful in auto-fluorescence diagnostic techniques, where the fluorescence of diseased tissue is known to differ from that of normal, tissue such that when illuminated with UV light, normal tissue reflects light of a different waveband when compared to light reflected from diseased tissue illuminated with the same UV light. Condensing lens 42 may be conventional and formed from glass or plastic. Alternatively, condensing lens 42 may take form in a static holographic optical element, or one or more electrically switchable holographic optical elements. Where condensing lens 42 takes form in one or more electrically switchable holographic optical elements, control and processing circuit 18 may be extended to provide the appropriate control signals. An exemplary condensing lens which takes the form of electrically switchable holographic optical elements is described in copending application serial No. 09/533,608 entitled Illumination System Using Optical Feedback which is incorporated herein by reference.

Light input to light guide 32 is transmitted through the endoscope where it emerges at a distal end on the distal end portion 14 as inspection light 44. Inspection light 44 illuminates a space into which the end portion 16 is inserted. Light 46 back scattered or reflected from the illuminated space falls incident upon a front surface 48 of electrically switchable holographic optical system 28. Electrically switchable holographic optical system 28, in response to control signals transmitted from control and processing circuit 18 via one or more conductors 38, diffracts and/or transmits the reflected light 46 to produce image light 52. Image light 52, or a portion thereof, is received the array of photo detectors of imaging device 26 (show in a cross sectional view in Figure 1). Imaging device 26, in response to timing signals or control signals received upon conductor(s) 36 from control and processing circuit 18, generates frames of image signals which are transmitted to control and processing circuit 18 via conductor(s) 34. Control and processing circuit 18, in turn, processes images signals from imaging device 26 to generate frames for display on video display 20. Accordingly, a user can view the illuminated space at the distal end via video display 20.

Figure 1 and subsequent figures show electrically switchable holographic optical system 28 and imaging device 26 positioned adjacent and external to the distal end portion 14 of endoscope 12. The present invention should not be limited thereto. Alternatively, one or both of the optical system 28 and imaging device 26 may be positioned within the passage of tube 24. Moreover, optical system 28 and imaging device 26 may be coupled to the other and contained within a housing which is releasably connected to the proximal end portion 16. Obviously, modification would need to be made in this alternative embodiment including devices of the housing which facilitate mating of conductors 24 through 38 to imaging device 26 and/or optical system 28. As a further alternative, optical system 28 and imaging device 26 may be contained within a tube having hardware which is mateable with corresponding hardware coupled to the distal end portion 14. In these alternative arrangements, the imaging device 26 and optical system 28 may be readily replaced if either malfunctions or if it is desired, for example, to replace one optical system with another having different optical characteristics. In any embodiment, it may be important to size the optical system 28 and/or imaging device 26 so as not to obstruct the emission of inspection light 44 from light guide 32.

Optical system 28 selectively transmits and/or diffracts reflected light 46 to perform one or more optical functions on the reflected light 46. More particularly, optical system 28 may filter, magnify, and/or focus reflected light 46 onto the input plane of image device 26 which contains the array of photo detectors. The optical system 28 is capable of operating upon reflected light 46 of a wide variety of bandwidths in the visible spectrum and in the near infrared. Moreover, imaging device 28 is also responsive to wavelengths in the visible spectrum and in the near infrared.

Figure 2 shows an alternative arrangement of the endoscopic system 10 shown in

Figure 1. Endoscopic system 60 shown in Figure 2 contains all the elements of the system 10 shown in Figure 1 except for the illumination system 22 and the light guide 32. Endoscopic system 60 operates similar to endoscopic system 10 described above. Endoscopic system 60 shown in Figure 2 may be used to view, via video display 20, hard to access areas which are sufficiently self-illuminated.

Figure 3 a shows an alternative endoscopic system embodiment employing the present invention. The endoscopic system 64 shown in Figure 3a includes many of the components found in the system of Figure 1. A major difference between systems 10 and 64 is that the annular core light guide 32 shown in the embodiment of Figure 1 is replaced by fiber optic bundles 66 in Figure 3a. Figure 3b shows an end view of the distal end portion 16 without the optical system 28. With reference to Figures 3a and 3b. fiber optic bundles 66a through 66d flank imaging device 26 in the distal end portion 14. Bundles 66a through 66d combine into one bundle 66 and receives focused light from the illumination system 22 at the proximal end portion 16. The focused light from illumination system 22 is transmitted by fiber optic bundle 66 until it is emitted as inspection light 44 at the ends of the fiber optic bundles 66a though 66d at the distal end portion 14. It is noted that bundle 66 is divided into four bundles 66a through 66d at the distal end 14. However, the present invention need not be limited to the arrangement shown in figures 3a and 3b. Rather, alternative arrangements can have bundle 66 dividing into two bundles, or more than four smaller bundles to provide a more uniform distribution of inspection light 44 on the area to be viewed. It is noted that in the alternative arrangements described herein, a light transparent window (not shown) may be provided at the proximate end to protect optical system 28, imaging device 26 or other components contained within or positioned adjacent the distal end portion 14.

In the systems shown in Figures 1 through 3, inspection light 44 emerges from the distal end portion of the endoscope to illuminate objects or area within the space being inspected. Light 44 reflected from objects in the field of view is collected by optical system 28 which forms an image in the plane of photodetectors of device 36. Imaging device 26, preferably a CCD, routes and possibly amplifies signals generated by the photo detectors. These signals, in turn, are transferred by conductor(s) 34 to control and processing electronics 18. Control and processing circuit 18 generates a video signal that drives a conventional video display 20 to provide a visible image of the space being inspected. Although not shown, it may be desirable to include light dispersing optics at the distal end portion 14 for dispersing inspection light 44 as it is emitted from light guide 32 or fiber optic bundles 66 to illuminate a wider field of view. The light dispersing objects may take form in one or more electrically switchable holographic optical elements controlled via signals or voltages transmitted from the control and processing electronics. Exemplary, dispersing optics employing electrically switchable holographic optical elements can be found in copending US Patent Application Serial No. 09/632,664, filed August 4, 2000, entitled Apparatus For Producing A Three Dimensional Image which is incorporated herein in its entirety.

Figure 4 shows yet another alternative endoscopic 70 which employs many of the elements set forth in the systems described in Figure 3. More particularly, endoscopic system 70 shown in Figure 4 includes optical system 28, imaging device 26 and optical bundle 66 shown in Figure 3. The imaging device 26 of Figure 4 is positioned adjacent to or within proximal end portion 16, and the fibers of the fiber optic bundle 66 do not divided into smaller bundles at the distal end portion 16. The endoscopic system 70 shown in Figure 4, like the system shown in Figure 2, is not equipped to transmit inspection light to the distal end portion 14. Rather, the endoscopic system 70 shown in Figure 4 is intended to view spaces or objects already sufficiently illuminated. Reflected light 46 is transmitted or diffracted by optical system 28 to produce image light 52 which is received by the ends of fiber optic bundle 66. Optical system 28 filters and/or focuses reflected light 46 onto the plane defined by the ends of the optical fibers of bundle 66. The image light is transmitted by fiber optic bundle 66 to proximal end portion 16 where it emerges therefrom as pixilated image light 72. Imaging device 26 receives pixilated image light 72 and generates corresponding image signals for further processing by control and processing electronics 18.

In a modified arrangement of the endoscopic system 70 shown in Figures 3 a and

3b, imaging device 26 is removed and optical system 28 is potentially reduced in size and repositioned in optical communication with one of the fiber optic bundles 66a through 66d. In this modified arrangement, image light 52 from the optical system may be transmitted via one of the fiber optic bundles 66a through 66d to an imaging device in optical communication with the fiber optic ends of the bundle at the proximal end. One or more of the remaining fiber optic bundles 66a through 66c may still be used to provide inspection light 44.

Figure 5 shows in block diagram form the switchable holographic optical system 28 coupled to control and processing circuit 18. Optical system is designed to perform one or more optical functions on the reflected light 46 in accordance with controlling signals and/or voltages from control and processing circuit 18. The optical functions include those performed by traditional optical devices such as lenses, prisms, mirrors, etc. The optical system 28 can also be designed to perform sophisticated optical functions on the reflected light such as varying the intensity of the image light 52, filtering one or more wavelengths of light from the reflected light, etc. The optical system is dynamic in that its optical functions are capable of modification in accordance with controlling signals and/or voltages from control and processing circuit 18. For example, the optics system may include one or more electrically switchable holographic optical elements that embody zooming lenses to magnify the image light, or select components thereof, onto imaging device 26 or the distal ends of optical fibers. These zooming lenses are variable focus lenses, which allow user control of image magnification. The optical system 28 may also include one or more electrically switchable holographic optical elements that embody focusing lenses to focus the image light 52, or components thereof, imaging device 26 or the distal ends of optical fibers. The optical system 28 may also function as a filter for filtering reflected light 46 to produce image light of one or more different wavebands including visible light. For example, where the inspection light 44 consists of the UV light mentioned above for use in auto-fluorescence diagnostic techniques, the optical system may include several switchable holographic optical elements each of which can filter different fluorescence bands (which will typically lie in the range extending from 500nm to the near infrared) of light 46 reflected from different tissues.

Figures 6A and 6B show exemplary alternative embodiments of electrically switchable holographic optical elements (SHOEs) 80a and 80b, respectively, which may be employed in the switchable holographic optical system 28 described above. In the preferred mode, optical system 28 will include several SHOEs. In one embodiment, optical system 28 may include three or more SHOEs 80a. In another embodiment, optical system 28 may include three or more SHOEs 80b. In still another embodiment, optical system 8 may include a combination of SHOEs 80a and 80b.

SHOE 80a of Figure 6A is shown in cross section and includes a pair of light transparent and electrically nonconductive layers 82, light transparent and electrically conductive layers 84, and a switchable holographic layer 86 formed, in one embodiment, from a polymer dispersed liquid crystal material described in US Patent Application 09/478,150 entitled Optical Filter Employing Holographic Optical Elements And Image Generating System Incorporating The Optical Filter, filed January 5, 2000. or US Patent Application 09/533,120 entitled Method And Apparatus For Illuminating A Display, filed March 23, 2000, both of which are incorporated herein by reference. In one embodiment, the substantially transparent, electrically nonconductive layers 82 comprises glass, while the substantially transparent electrically conductive layers 84 are formed from indium tin oxide (ITO). Layers 82 through 86 are arranged on a common optical axis like a stack of pancakes between a front surface 90 and a back surface 92. Holographic layer 86 may be formed from a polymer dispersed liquid crystal mixture which undergoes phase separation during a hologram recording process, thereby creating fringes which include regions densely populated by liquid crystal micro-droplets interspersed with regions of clear polymer. The holographic layer 86, and thus the SHOE 80a, operates between active and inactive states depending upon whether a voltage is applied to ITO layers 84. In the active state, no voltage is applied to ITO layers 84, and holographic layers 86 diffracts a narrow bandwidth of light incident thereon in a predetermined manner while transmitting the remaining bandwidths of incident light without substantial alteration. In the inactive state, ITO layers 84 are coupled to a voltage source of sufficient magnitude. With ITO layers 84 connected to the voltage source an electric field is established within holographic layer 86 which changes the natural orientation of the liquid crystal droplets causing a refractive index modulation of fringes to reduce and the hologram diffraction efficiency to drop to a very low level, effectively erasing the hologram. In this inactive state, substantially all incident light is transmitted by holographic layer 86 without substantial alteration.

The holograms recorded in holographic layer 86 are preferably volume holograms, also known as thick or Bragg holograms. Thin phase holograms may also be employed. However, the use of Bragg holograms is preferred because they offer higher diffraction efficiencies for incident light whose wave length is close to the theoretical wavelength satisfying the Bragg diffraction condition, and which is within a few degrees of the theoretical angel which also satisfies the Bragg diffraction condition.

SHOE 80a may be either transmissive or reflective. Indeed, optical system 28 may employ combinations in which some of the SHOEs are reflective and some of the SHOEs are transmissive. In reflective type SHOEs, diffracted light emerges from the same surface upon which the SHOE receives light. Thus, with reference to Figure 6a, light incident on surface 90 and subsequently diffracted by holographic layer 86, emerges from the same surface 90. In contrast, light diffracted in transmissive type SHOEs emerge from an opposite surface upon which the SHOE receives incident light. Thus, with reference to Figure 6a, light received on surface 90 and subsequently diffracted by holographic layer 86 emerges from back surface 92.

The holograms recorded in holographic layer 86, when active, diffract incident light in a predetermined manner to perform one of many optical functions performed by traditional optical elements such as lenses, mirrors, filters, prisms, etc. For example, a hologram recorded in holographic layer 86 may focus a narrow bandwidth of incident light when SHOE 80a is active. A hologram recorded in holograph layer 86 may be configured to disperse a narrow bandwidth of incident light when operating in the active state. Further, the hologram recorded in hologram layer 86 may deflect out incident light of a particular wavelength band when active thereby operating as a filter. With more than one SHOE 80a included in switchable holographic optical system 28, optical system 28 may perform a variety of optical functions.

SHOE 80b illustrated in cross section in figure 60b is similar in structure to the SHOE 80a shown in Figure 6a. More particularly, SHOE 80b includes transparent and electrically nonconductive layers 82 (i.e. glass) and a pair of transparent and electrically conductive layers 84 (ITO layers). In contrast to SHOE 80a shown in Figure 6a, SHOE 80b includes three distinct holographic layers 86a through 86c. It is noted that fewer than or more than three layers holographic layers 86 may be employed in SHOE 80b. In the embodiment of Figure 6b, when a voltage source is applied to ITO layers 84, all three holographic layers 86a through 86c operate in the inactive state and transmit substantially all light incident thereon through without substantial alteration. When the holograms of holographic layers 86a through 86c operate in the active state (when ITO layers are disconnected from the voltage source), each of the holograms may diffract the same or different bandwidths of visible light incident thereon. For example, holographic layers 86a through 86c may be designed to diffract red, green, and blue bandwidths, respectively, of visible light. Alternatively, each of the holographic layers 86a through 86c may record a hologram designed to diffract the same or different bandwidths of a particular primary color, e.g., red visible light.

Holographic layers 86a through 86c can be either transmissive, reflective or a combination of both. It is well know that reflective type holograms are responsive to a narrower bandwidth of light when compared to transmissive type holograms. SHOE 80b may embody a reflective type filter in which each of the holographic layers 86a through 86c diffract different wavelength bands of, for example, red visible light such that only green and blue visible bandwidth light are transmitted therethrough.

Figures 7a through 7c illustrate operational aspects of switchable holographic optical system 28 employing three distinct reflective type SHOEs shown in Figures 6a or 6b. More particularly, figures 7a through 7c show SHOEs 100R, 100G, and 100B, each of which is configured to diffract, when active, a portion of or all light in the visible red, green, and blue bandwidths. respectively. The SHOEs 100R, 100G, and 100B of Figures 7a through 7c will be described as configured to diffract all of the red, green, and blue bandwidths, respectively, of reflected light 46 when operating in the active state.

Figures 7a through 7c show optical system as it operates in a three stage cycle in accordance with control signals and/or voltages from control and processing circuit 18 . In the first stage, as shown in Figure 7a, SHOEs 100R and 100G are activated while SHOE 100B is inactive. In this cycle, activated SHOEs 100R and 100G diffract all of the red and green bandwidths, respectively, of reflected light 46. The diffracted red and green light emerges as lights 102R and 102G, respectively. The remaining portion of reflected light 46 pass through SHOEs 100R, 100G, and 100B to emerge from optical system 28 as blue bandwidth image light 52B. Imaging device 26 (not shown in Figures 7a through 7c) converts this blue image light 52B into corresponding signals which are transmitted to control and processing circuit 18 for further processing into a frame which can be displayed on video display. In the second cycle, as shown in Figure 7b, control signals deactivate SHOE 100G while activating SHOE 100B. Here, activated SHOEs 100R and 100B diffract all of the red visible and blue visible bandwidths, respectively, of reflected light 46. The remaining portion of reflected light 46 pass through SHOEs 100R, 100G, and 100B to emerge from optical system 28 as green bandwidth image light 52G. Imaging device 26 converts this green bandwidth image light into corresponding signals which are transmitted to control and processing circuit 18 for further processing into a frame which can be displayed on video display. In the last cycle, control signals provided by control processing circuit 18 deactivates SHOE 100R and activates SHOE 100G, while SHOE 100B is maintained in the active state. In this configuration optical system 28 diffracts all of the green and blue bandwidth portions of reflected light 46 thereby producing image light 52R which consists mainly of the red bandwidth portion of reflected light 46. Imaging device 26 converts this red bandwidth image light 52R into corresponding signals which are transmitted to control and processing circuit 18 for further processing into a frame which can be displayed on video display. The cycles represented in Figures 7a through 7c are repeated such that imaging device sequentially generates image signals corresponding to blue, green, and red bandwidth portions of the reflected light 46. The three stage cycle is repeated quickly so that the frames produced in each cycle are displayed on the video display and eye integrated into a tristimulus image.

Figures 8a through 8c represent operational aspects of a holographic optical system 28 formed of three of transmissive type SHOEs 104R. 104G, and 104B. SHOEs 104R through 104B may take form in the SHOE shown in Figures 6a or 6b. The optical system 28 shown in Figures 8a through 8c operate substantially the same as described with reference to the SHOE 28 in Figures 7a through 7c.

Figures 9 through 12 illustrate alternative embodiments of optical system 28. Figure 9 shows optical system 28 of Figures 7a through 7c extended to include three transmissive type SHOEs 106R, 106G. and 106B which function as lenses to focus image light 52 onto the array of photodetectors of the imaging device (not shown). SHOE 106, when active, diffracts red bandwidth light. SHOE 106G. when active, diffracts green bandwidth light. SHOE 106B, when active, diffracts blue bandwidth light. Each of the respective SHOEs 106R through 106B may take form in SHOE 80a or SHOE 80b described in Figures 6A and 6B, respectively. In an alternative embodiment, SHOEs 106R through 106B may be replaced by one SHOE as shown in Figure 6B wherein the holographic layers 86a, 86b, and 86c, are designed to diffract red, green, and blue bandwidth light, respectively. This alternative form of the optical system of Figure 9 would require a lesser number of control signals from control and processing circuit 18.

SHOE 28 shown in Figure 9 operates in a three stage cycle similar to that described with reference to figures 7a through 7c and Figures 8a through 8c. Figure 9 shows the first cycle of the three stage cycle. In this stage, control signals received from the control and processing circuit 18 activate SHOEs 100R, 100G and 106B while deactivating the remaining SHOEs. In this configuration. SHOEs 100R and 100G filter out the red and green bandwidth portions of reflected light 46. The remaining blue bandwidth portion of reflected light 46 transmits through SHOEs 100B, 100R, and 100G until it is diffracted by activated SHOE 108B. SHOE 108b as noted above, focuses the blue light when active. More particularly, the holographic layer in SHOE 106B records a hologram of a conventional lens which operates on blue bandwidth light incident thereon.

Figure 10 shows the optical system 28 of Figure 9 extended to include SHOEs

108R through 108b. SHOEs 108R through 108b may take form in either SHOE 80a or 80b or Figures 6A or 6B, respectively. SHOEs 108R through 108b, like SHOEs 106R through 106B, when active, diffract and focus red through blue bandwidths, respectively, of visible light. SHOEs 106R through 106 B of Figure 10 may be replaced by one SHOE as shown in Figure 6B wherein the holographic layers 86a, 86b, and 86c thereof, are designed to diffract red, green, and blue bandwidth light, respectively. Optical system 28 shown in Figure 10 operates in a three stage cycle similar to that described in Figure 9. Figure 10 shows optical system 28 operating in the first stage whereby control and processing circuit 18 activates SHOEs 100R, 100G, 106B and 108B while maintaining the remaining SHOEs in the inactive state. In this stage of the three stage cycle, SHOEs 100R and 100G filter out the red and green bandwidth portions of reflected light 46 while transmitting the blue bandwidth portion. Activated SHOEs 106B and 18B cooperatively focus the remaining blue bandwidth portion of reflected light 46 onto the plane of photodetectors of the imaging device. Optical system 28 shown in Figure 10 is capable magnifying its field of view.

Figure 11 shows the SHOE 28 of Figure 9 with the reflective type SHOEs 100 replaced with transmissive type filter SHOEs 104 shown in Figures 8a through 8c. The optical system 28 shown in Figure 11 operates in a matter substantially equal to that described with reference to the optical system 28 shown in Figure 9.

Figure 12 shows yet another alternative embodiment of the optical system 28. Essentially, optical system 28 of Figure 12 includes only the transmissive type SHOEs 106 described with reference to Figures 9 through 11. The optical system 28 shown in Figure 12 may operate in one mode whereby each SHOE 106R. 106G, and 106B is simultaneously activated and to diffract the red, green, and blue bandwidths, respectively, of reflected light 46.

Although the present invention have been described in connection with several embodiments, the invention is not intended to be limited to the specific forms set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as can be reasonably included with in the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising: a tube extending between first and second ends; a first switchable holographic optical element (SHOE), wherein the first SHOE operates between active and inactive states, wherein the first SHOE, when active, diffracts first bandwidth light incident thereon, and wherein the first SHOE, when inactive, transmits first bandwidth light incident thereon without substantial alteration; a first conductor coupled to the first SHOE, wherein a portion of the first conductor extends within the tube between the first and second ends thereof, and wherein the first conductor is configured to transmit control signals for switching the first SHOE between the active and inactive states.

2. The apparatus of claim 1 further comprising: an imaging device comprising an array of light detectors, wherein the imaging device is configured to generate electrical signals in response to receiving light; a second conductor coupled to the imaging device, wherein a portion of the second conductor extends within the tube between the first and second ends thereof, and wherein the second conductor is configured to transmit electrical signals generated by the imaging device.

3. The apparatus of claim 2 wherein each of the tube, first conductor, and second conductor is flexible.

4. The apparatus of claim 3 wherein the first SHOE is in optical communication with the imaging device.

5. The apparatus of claim 4 further comprising a flexible light guide, wherein a portion of the light guide is contained within the tube and extends between first and second ends thereof, and wherein the light guide is configured to transmit light therethrough.

6. The apparatus of claim 2 further comprising a flexible light guide, wherein portion of the light guide is contained within the tube and extends between first and second ends thereof, and wherein the light guide is configured to transmit light therethrough, and wherein the first SHOE is in optical communication with the light guide.

7. The apparatus of claim 5 further comprising: a second SHOE positioned adjacent the first SHOE, wherein the second SHOE operates between active and inactive states, wherein the second SHOE, when active, diffracts second bandwidth light incident thereon, and wherein the second SHOE, when inactive, transmits second bandwidth light incident thereon without substantial alteration a third SHOE positioned adjacent the second SHOE, wherein the third SHOE operates between active and inactive states, wherein the third SHOE, when active, diffracts third bandwidth light incident thereon, and wherein the third SHOE, when inactive, transmits third bandwidth light incident thereon without substantial alteration wherein the first SHOE, when active or inactive, transmits second and third bandwidth light without substantial alteration; wherein the second SHOE, when active or inactive, transmits first and third bandwidth light without substantial alteration; wherein the third SHOE, when active or inactive, transmits first and second bandwidth light without substantial alteration; wherein first, second, and third bandwidth lights are different from each other, and; wherein the first, second, and third SHOEs are in optical communication with each other.

8. The apparatus of claim 1 wherein the first SHOE is configured to switch between the active and inactive states in less than 150 microseconds.

9. The apparatus of claim 1 wherein the first SHOE comprises a holographic recording medium that records a hologram, wherein the holographic recording medium comprises: a monomer dipentaerythritol hydroxypentaacrylate; a liquid crystal; a cross-linking monomer; a coinitiator; and a photoinitiator dye.

10. The apparatus of claim 1 wherein the first SHOE comprises a hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure: a polymerizable monomer; a liquid crystal; a cross-linking monomer; a coinitiator; and a photoinitiator dye.

11. The apparatus of claim 5 further comprising a second SHOE in optical communication with the first SHOE, wherein the second SHOE operates between active and inactive states, wherein the second SHOE, when active, diffracts first bandwidth light incident thereon, and wherein the second SHOE, when inactive, transmits first bandwidth light incident thereon without substantial alteration.

12. The apparatus of claim 5 further comprising: a second SHOE in optical communication with the first SHOE, wherein the second SHOE operates between active and inactive states, wherein the second SHOE, when active, diffracts second bandwidth light incident thereon, and wherein the second SHOE, when inactive, transmits second bandwidth light incident thereon without substantial alteration; wherein each of the first and second SHOEs comprises oppositely facing front and back surfaces; wherein the first SHOE, when operating in the active state, is configured to diffract first bandwidth light received on the front surface of the first SHOE thereby producing diffracted first bandwidth light, wherein the diffracted first bandwidth light emerges from the front surface of the first SHOE; wherein the second SHOE, when operating in the active state, is configured to diffract second bandwidth light received on the front surface of the second SHOE thereby producing diffracted second bandwidth light, wherein the diffracted second bandwidth light emerges from the back surface of the second SHOE.

13. The apparatus of claim 12 further comprising a third SHOE in optical communication with the first and second SHOEs. wherein the third SHOE operates between active and inactive states, wherein the third SHOE, when active, diffracts second bandwidth light incident thereon, and wherein the third SHOE, when inactive, transmits second bandwidth light incident thereon without substantial alteration, wherein the third SHOE is configured to receive the diffracted second bandwidth light produced by the second SHOE, and wherein the third SHOE, when active, is configured to diffract the received diffracted second bandwidth light.

14. The apparatus of claim 12 wherein the second SHOE, when active, is configured to focus first bandwidth light by diffraction onto a plane of the image detector containing the array of photodetectors.

15. The apparatus of claim 12 wherein the second SHOE, when active, is configured to deflect first bandwidth light by diffraction onto a plane of the image detector containing the array of photodetectors.

16. The apparatus of claim 6 wherein the first SHOE is configured to diffuse first bandwidth light transmitted through the light guide.

17. The apparatus of claim 1 further comprising a fiber optic bundle, a portion of which is contained within the tube extending between first and second ends thereof, wherein the fiber optic bundle is configured to transmit light therethrough.

18. The apparatus of claim 17 further comprising an imaging device comprising an array of light detectors, wherein the imaging device is configured to receive light transmitted through the fiber optic bundle, and wherein the imaging device is configured to generate electrical signals in response to receiving light transmitted through the fiber optic bundle.

19. The apparatus of claim 1 further comprising a second tube, wherein the second tube is flexible and extends from a first end to a second end, and wherein the first end of the second tube is releasably connected to the first end of the tube, and wherein another portion of the first conductor extends through the second tube between the first and second ends thereof.