WO2001029588A1

WO2001029588A1 - Inspection device

Info

Publication number: WO2001029588A1
Application number: PCT/US2000/029240
Authority: WO
Inventors: Milan M. Popovich
Original assignee: Digilens, Inc.
Priority date: 1999-10-21
Filing date: 2000-10-23
Publication date: 2001-04-26
Also published as: AU1226101A

Abstract

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, a light guide, and a first conductor coupled to the first SHOE. The first SHOE is in optical communication with the light guide. 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 first and second ends thereof, transmits control signals or a controllable voltage for switching the first SHOE between the active and inactive states.

Description

INSPECTION DEVICE

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Serial No. 60/160.802 filed October 21, 1999. This application is also a continuation-in-part of U.S. Patent Application Serial No. 09/675,431 (Attorney Docket Number M-9228 US) entitled Inspection Device Containing Switchable Holographic Optical System filed September 29, 2000.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to inspection devices for inspecting hard to access areas. More particularly, the present invention relates to an inspection device employing a switchable holographic optical element (SHOE) system. The present invention may find widespread application. 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.

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. The image is transferred through the 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 of the image, 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 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 a flexible fiber optic bundle contained within flexible tubing. A dispersing conventional optical element formed from glass or other static material, is positioned at the tip of the fiber optical bundle and 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, a light guide, and a first conductor coupled to the first SHOE. The first SHOE is in optical communication with the light guide. 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. The signals generated by the imaging device maybe transferred over the second conductor to. for example, processing circuitry

.9. which processes the signals 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, the light guide, the first conductor, and the 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 one embodiment of an endoscope employing the present invention;

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

Figure 3 A is a cross sectional view of one embodiment of an ESHOE employable in the optical system shown in Figures 1 and 2;

Figure 3B is a cross sectional view of a second embodiment of an ESHOE employable in the optical system shown in Figures 1 and 2;

Figure 4A is an end view of the endoscope shown in Figures 1 and 2;

Figure 4B is a block diagram of the control and processing circuit coupled to a cross sectional view of one embodiment of the optical system employed in the systems of Figures 1 or 2;

Figure 4C is a block diagram of the control and processing circuit coupled to a cross sectional view of another embodiment of the optical system employed in the systems of Figures 1 or 2.

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 only distal and proximal end portions 14 and 16, respectively, are illustrated. 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 (optical system) 28. The imaging device 26 may take form in an array of photodetector elements which convert incident light into corresponding electrical signals. Preferably, the imaging device takes form in a CCD array. The present invention should not be limited thereto. Rather, the present invention contemplates alternative imaging devices including those which contain arrays of photocapacitors. photoresistors, etc.

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 cylindrical 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. Annular core section 32 may be referred to as light guide 32. Conductors 34 through 38 function to transmit control signals, image 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 also couple 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 image light. 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 for controlling the dynamic characteristics of the optical system 28 as will be more fully described below. Alternatively, the 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 and/or switching voltages 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 conductors 36. In this alternative arrangement, there may be no need for one or more conductors 38.

Illumination system 22 includes a light source 40 and. optionally, a condensing lens 42. Illumination system 22 is positioned adjacent the proximal end 16 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 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 (not shown) formed of one or more switchable holographic optical elements described in U.S. Patent Application 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) described in Projection System Based On

Reconfigurable Holographic Optics. 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 source 40 may produce or the switchable filter mentioned above may filter light from a light emitting device to produce near UV/blue light (typically, incoherent or laser light in the range 400 to 450 nm) or infrared for input to condensing lens 42 or light guide 32. 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. More particularly, when illuminated with near UV/blue light, light reflected from normal tissue has a different waveband when compared to light reflected from diseased tissue illuminated with the same near UV/Blue 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 U.S. Patent Application 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 and is subsequently received by optical system 28 as illumination light 44. Optical system 28 spreads or diffuses illumination light 44 depending on control signals and/or switching voltages provided by control and processing circuit 18 via one or more conductors 38 as will be more fully described below. Inspection light 44. once spread or dispersed by optical system 28, illuminates a space into which the distal end portion 14 is inserted.

Thus, a wider field of view of the imaging device 26 is illuminated with illumination light that has been spread or diffused by optical system 28. Light 46 back scattered or reflected from the illuminated space falls incident upon imaging device 26. A lens or lens array (not shown) may be included with imaging device 26. This lens or lens array may be positioned to receive and focus reflected light 46 onto the plane of detectors of device 26 thereby forming an image of the space illuminated by light 44 that can be converted into image signals. The lens or lens array may be static and take form in one or more conventional optical components made of glass, plastic or other light transmissive material. Alternatively, the lens or lens array may take form in one or more static or dynamic holographic optical elements including those described in U.S. Patent Application Serial No. 09/675,431.

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 cylindrical passage of tube 24. Moreover, optical system 28 and imaging device 26 may be coupled together and contained within a housing which is releasably connected to the distal end portion 14. A releasably connected housing which contains the imaging device 26 and/or optical system 28 would include means 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 flexible or rigid 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 imaging device 26 so as not to obstruct the emission of illumination light 44 from light guide 32 or optical system 28.

As noted above, optical system 28 spreads or diffuses light 44 depending on control signals and/or switching voltages provided by control and processing circuit 18. In one embodiment, optical system 28 may include a single electrically switchable holographic optical element more fully described below. In another embodiment, optical system 28 may include several electrically switchable holographic optical elements more fully described below.

In the embodiment shown in Figure 1 (and in Figure 2A), optical system 28 includes optical subsystems 28a-28c, more fully described below, each of which is operative to alter the characteristics of light received from light guide 32 in a different way when activated. For example, optical subsystem 28c, when activated, may diffract light from light guide 32 and produce illumination light 44c with a relatively wide spread. Optical subsystem 28b, when activated, may diffract light from light guide 32 and produce illumination light 44b with a relatively narrow spread when compared to the light spread of illumination light 44c. It is noted that light 44b may illuminate a wider field of view of imaging device 26 when compared to field of view illuminated by passing through optical system 28 without alteration or substantial alteration. Further, it is noted that an additional optical subsystem may be added that diffracts light emitted from light guide 32 to produce a focused beam of illumination light. Optical subsystem 28a, when activated, may diffract light from light guide 32 and produce diffused illumination light (not shown in Figure 1) which may fully illuminate the space into which the proximal end 14 is inserted. Each of the optical subsystems 28a-28c is independently switchable between active and inactive states in accordance with control signals and/or switching voltages provided by control and processing circuit 18.

Figure 2A shows an alternative endoscopic system 50 employing the present invention. The endoscopic system 50 shown in Figure 2A includes many of the components found in the system 10 of Figure 1. A major difference between systems 10 and 50 is that the flexible light guide 32 shown in Figure 1 is replaced by optical fibers in Figure 2A. Figure 2B shows an end view of the distal end portion 16 without the optical system 28.

With reference to Figures 2A and 2B, fiber optic bundles 50a through 50d flank imaging device 26 in the distal end portion 14. Bundles 50a through 50d combine into one bundle 50. Bundle 50 receives focused light from the illumination system 22 at the proximal end portion 16. The focused light from illumination system 22 is transmitted by the optical fibers until it is emitted as inspection light 44 at the ends of the fiber optic bundles 50a though 50d at the distal end portion 14. It is noted that bundle 50 is divided into four bundles 50a through 50d at the distal end 14. However, the present invention need not be limited to the arrangement shown in figures 2A and 2B. Rather, alternative arrangements can have bundle 50 dividing into two bundles, or more than four smaller bundles to provide a more uniform distribution of illumination light 44 on the area to be viewed. Moreover, the distal ends of optical fibers of bundle 50 can be arranged to form a ring around imaging device 26. 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. It is also noted that the endoscopic systems shown in Figures 1 and 2 may also include a second optical system through which reflected light 46 is filtered or otherwise altered before reaching imaging device 26 as is more fully described in U.S. Patent Application Serial No. 09/675,431( Attorney Docket Number M-9228 US) entitled Inspection Device Containing Switchable Holographic Optical System filed September 29. 2000.

In the systems shown in Figures 1, 2A. and 2B, inspection light 44 emerges from the optical system 28 to illuminate objects or area within the space being inspected. Photodetectors of device 26 collect and convert reflected light 46 reflected from illuminated objects in the field of view of the imaging device 26. Imaging device 26. preferably a CCD. routes and possibly amplifies image signals generated by the photo detectors thereof. 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.

Figures 3 A and 3B show exemplary alternative embodiments of electrically switchable holographic optical elements (ESHOEs) 60a and 60b. respectively, which may be employed in the optical subsystems 28a-28c described above. In one embodiment, each optical system group 28a-28c may include one or more ESHOEs 60a or 60b.

ESHOE 60a of Figure 3A is shown in cross section and includes a pair of light transparent and electrically nonconductive layers 62, light transparent and electrically conductive layers 64. and a switchable holographic layer 66 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 62 may take form in clear glass or plastic, while the substantially transparent electrically conductive layers 64 may take form in a thin layer of indium tin oxide (ITO). Layers 62 through 66 are arranged on a common optical axis like a stack of pancakes between a front surface 70 and a back surface 72. Holographic layer 66 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 66, and thus the ESHOE 60a, operates between active and inactive states depending upon whether a voltage is applied to ITO layers 64. In the active state, no voltage is applied to ITO layers 64. and holographic layer 66 diffracts a narrow bandwidth of light incident thereon in a predetermined manner while transmitting the remaining bandwidths of incident light without alteration or substantial alteration. In the inactive state, ITO layers 64 are coupled to a voltage source of sufficient magnitude. With ITO layers 64 connected to the voltage source an electric field is established within holographic layer 66 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, all or substantially all incident light is transmitted by holographic layer 66 without alteration or substantial alteration.

The holograms recorded in holographic layer 66 are preferably transmissive type. Further, the holograms recorded in layer 66 are volume holograms, also known as thick phase or Bragg holograms. Thin phase holograms may also be employed. However, the use of Bragg type 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.

The holograms recorded in holographic layer 66, when active, diffract incident light in a predetermined manner thereby performing one or more of many optical functions performed by traditional optical elements such as lenses. For example, a hologram recorded in holographic layer 66 may spread or diverge a narrow bandwidth of incident light over a predefined field of view when ESHOE 60a is active. A hologram recorded in holograph layer 66 may be configured to diffuse a narrow bandwidth of incident light when operating in the active state. It is known that transmission type holograms are sensitive to the polarization state of light incident thereon. In particular, the diffraction efficiency is much higher for p- polarized light than for s-polarized light, with the result that the s-polarized component of the incident tends to pass through the holographic layer 66 unaffected and. in a sense, is wasted. U.S. Patent Application 09/478,150 filed January 5. 2000 and entitled Optical Filter Employing Holographic Optical Elements And Image generating System Incorporating The Optical Filter, which is incorporated herein by reference, describes various ways of overcoming this problem, so that both the p- and s-polarized components of the incident light are fully diffracted.

Figure 3B shows an alternative ESHOE 60b which diffracts both the p- and s- polarized components of incident light. ESHOE 60b illustrated in cross section in Figure 3B is similar in structure to the ESHOE 60a shown in Figure 3 A. More particularly, ESHOE 60b includes light transparent and electrically nonconductive layers 62 (i.e. clear glass or plastic) and a pair of transparent and electrically conductive layers 64 (ITO layers). In contrast to ESHOE 60a shown in Figure 3 A. ESHOE 60b includes two distinct holographic layers 66p through 66s. In the embodiment of Figure 3B, when a voltage source is applied to ITO layers 64, both holographic layers 66p and 66s operate in the inactive state and transmit substantially all light incident thereon through without substantial alteration. When the holograms of holographic layers 66p and 66s operate in the active state (when ITO layers are disconnected from the voltage source), each of the holograms may diffract different components of the same bandwidths of light incident thereon. For example, holographic layers 66p and 66s may be designed to diffract the p and s-polarized components, respectivley, of light incident thereon. With holographic layer 66p activated, substantially all of the p-polarized component of a narrow band of light incident on front surface 70 is diffracted while the s-polarized component passes without substantial alteration. Similarly, with holographic layer 66s activated, substantially all of the s-polarized component of the narrow band of light incident thereon is diffracted while the p-polarized component passes to the back surface 72 without substantial alteration. The use of ESHOEs 60b in optical subsystems 28a-28c is preferred since ESHOEs 60b diffract a greater portion of incident light when compared to ESHOE 60a. Alternatively, each of the optical subsystems 28a-28c may employ at least two ESHOEs 60a, one of which is configured to diffract p-polarized incident light while the other is configured to diffract s-polarized incident light.

Figure 4A shows a end view of optical system 28 and imaging device 26. Figure 4B shows control and processing circuit 18 coupled to a cross sectional view of one embodiment of the optical system 28. Figure 4C shows a cross sectional view of another embodiment of he optical system 28. Figures 4A through 4C show that in one embodiment, optical system 26 can be annular in shape with a central passage containing imaging device 26.

As noted above, each optical subsystem 28a-28c may include one or more of the ESHOEs 60a or 60b shown in Figures 3 A or 3B, respectively. Preferably, as noted above, each of the subsystems 28a-28c includes one or more ESHOEs 60b. Each of the optical subsystems 28a-28c of Figure 4B includes one ESHOE 60b configured to diffract a narrow bandwidth of incident light. For example, the ESHOE 60b in each of the subsystems 28a-28c of Figure 4B is designed to diffract infrared or near UV/Blue light when active. When optical system 28 of Figure 4B is used in the endoscopic system of Figures 1 or 2, illumination system 22 would preferably produce only narrow bandwidth light (e.g., infrared or near UV/Blue light) for subsequent diffraction by an activated ESHOE 60b of one of the subsystems 28a-28c. In Figure 4B. subsystem 28c is shown activated and producing illumination light 44c.

In alternative embodiment shown in Figure 4C. each of the subsystems 28a-28c include three ESHOEs 60b. More particularly, each subsystem 28a-28c in Figure 4C includes ESHOEs 60br. 60bg. and 60bb designed to diffract red, green, and blue bandwidths, respectively, of visible light when active. When optical system 28 of Figure 4C is used in the endoscopic system of Figure 1 or 2. illumination system 22 sequentially and cyclically emits red, green, and blue visible bandwidth light for subsequent diffraction. At any point in time during the operation of optical system 28 of Figure 4C. only one ESHOE. 60bg, or 60bb of one subsystem 28a, 28b. or 28c is active. The activation and deactivation of the ESHOEs in one subsystem are timed so that ESHOE 60br is activated while ESHOEs 60bg and 60bb are deactivated and illumination source 22 generates red bandwidth light, ESHOE 60bg is activated while ESHOEs 60br and 60bb are deactivated and illumination source 22 generates green bandwidth light, and ESHOE 60bb is activated while ESHOEs 60br and 60bg are deactivated and illumination source 22 generates blue bandwidth light. This cycle is repeated rapidly in accordance with control signals and/or switching voltages provided by control and processing circuit 18 so as not to be detected by an eye of a user, who perceives the output of optical system 28, whether spread or diffused, to be effectively composed of white light.

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; a 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; wherein the first SHOE is in optical communication with the light guide.

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, second conductor, and light guide is flexible.

4. The apparatus of claim 3 wherein the first SHOE is configured to receive light transmitted by the light guide.

5. The apparatus of claim 1 further comprising: a second SHOE positioned adjacent the first SHOE; wherein the first SHOE, when active, is configured to diffract a p-polarized light component of the first bandwidth when operating in the active state while transmitting an s-polarized light component of the first bandwidth without substantial alteration; wherein the second SHOE operates between active and inactive states, wherein the second SHOE, when active, diffracts an s-polarized component of first bandwidth light incident thereon while transmitting a p-polarized light component of first bandwidth light incident thereon, and wherein the second SHOE, when inactive, transmits second bandwidth light incident thereon without substantial alteration.

6. The apparatus of claim 1 wherein the light guide comprises flexible optical fibers.

7. The apparatus of claim 1 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.

1 1 1. The apparatus of claim 1 further comprising a second SHOE in optical

2 communication with the first SHOE, wherein the second SHOE operates between active

3 and inactive states, wherein the second SHOE, when active, diffracts first bandwidth light

4 incident thereon, and wherein the second SHOE, when inactive, transmits first bandwidth

5 light incident thereon without substantial alteration.

1 12. The apparatus of claim 2 further comprising a second SHOE in optical

2 communication with the image generator, wherein the second SHOE operates between

3 active and inactive states, wherein the second SHOE, when active, diffracts first

4 bandwidth light incident thereon, and wherein the second SHOE, when inactive.

5 transmits first bandwidth light incident thereon without substantial alteration.

6 13. The apparatus of claim 1 wherein the first SHOE is annular in cross

7 section.

1 14. The apparatus of claim 12 wherein the second SHOE, when active, is

2 configured to focus first bandwidth light by diffraction onto a plane of the image

3 detector containing the array of photodetectors.

1 15. The apparatus of claim 1 wherein the first SHOE, when active, is

T configured to spread first bandwidth light transmitted through the light guide.

1 16. The apparatus of claim 1 wherein the first SHOE is configured to diffuse

9 first bandwidth light transmitted through the light guide.

3 17. The apparatus of claim 1 further comprising a light source configured to

4 generate light, wherein light generated by the light source is input to the light guide.

1 18. The apparatus of claim 1 wherein the imaging device is configured to

? receive first bandwidth light reflected from objects illuminated by first bandwidth light

J diffracted by the first SHOE.

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.