Miniature image acquistion system using a scanning resonant waveguide

A minimally invasive, medical, image acquisition having a flexible optical fiber serving as an illuminating wave guide. In one resonance mode, the distal end of the fiber is a stationary node. The fiber includes a lens at the distal tip which collimates emitted light. A scan lens is positioned off the end of the fiber. The relative magnifications of the lenses and the relative positions determines the pixel resolution. In particular, the illumination fiber outputs a light beam or pulse which illuminates a precise spot size. A photon detector detects reflected photons from the object, including the spot. Pixel resolution is determined by the area of the illumination spot (and thus the lens configuration), rather than an area sensed by the detector.

BACKGROUND OF THE INVENTION
 This invention relates to fiber optic scanning devices, such as fiber optic
 image acquisition devices and fiber optic image display devices, and more
 particularly to a fiber optic scanning device which achieves a high image
 resolution and a wide field of view using a flexible fiber of very small
 diameter.
 Fiber optic image acquisition devices include endoscopes, boroscopes and
 bar code readers. An endoscope is an imaging instrument for viewing the
 interior of a body canal or hollow organ. Entry typically is through a
 body opening. A boroscope is an imaging instrument for viewing an internal
 area of the body. Entry typically is invasive through a `bored` opening
 (e.g., a surgical opening).
 There are rigid endoscopes and flexible endoscopes. Rigid endoscopes do not
 have a pixelated image plane. Flexible endoscopes are smaller and
 conventionally have a pixelated image plane. Flexible endoscopes, however,
 are unable to achieve the resolution and field of view of rigid
 endoscopes. But the rigid endoscopes are unable to be used in many
 applications where small size and flexible fibers and shafts are required.
 The goal of any endoscope is high image quality in a small package,
 allowing minimal tissue trauma. In the growing field of minimally invasive
 surgical techniques, there is great demand for smaller endoscopes that
 match current image quality. In particular, the demand for minimally
 invasive medical procedures has increased the demand for ultrathin optical
 endoscopes. However, commercial flexible endoscopes have a fundamental
 tradeoff of size versus image quality. The smaller the endoscope diameter
 the lower the image resolution and/or field-of-view (FOV), such that image
 quality deteriorates. Many endoscopic techniques are not possible or
 become risky when very small endoscopes are used because the doctor has
 insufficient visual information, i.e. small size and poor quality of
 images. Accordingly, there is a need for very small, flexible endoscopes
 with high resolution and FOV. This fundamental tradeoff of a flexible
 image generator that has both a very small diameter and has the high image
 quality is a major limitation in applications outside the human body, such
 as remote sensing.
 Conventional flexible endoscopes and boroscopes include a large spatial
 array of pixel detectors forming a CCD camera. Typically a bundle of
 optical fibers capture an image and transmit the image to the CCD camera.
 To achieve a high resolution, wide field image, such CCD cameras often
 include a pixel detector array of approximately 1000 by 1000 detectors.
 For color fidelity it is common to include three such arrays, and where
 stereoscopic viewing is desired, this doubles to six arrays. A fiber is
 present for each pixel detector. Each fiber has a diameter greater than or
 equal to 4 microns. Thus, acquisition requires a space of greater than or
 equal to 4 microns per pixel. If a standard sVGA image is desired
 (800.times.600 pixels), then a minimum diameter of just the image conduit
 is greater than 3 mm. A 1000 by 1000 pixel detector array has a diameter
 of at least 4 mm. For a VGA standard, resolution and/or field of view is
 sacrificed by having fewer pixel elements in order to attain less than 3
 mm overall diameter scopes. Reducing the diameter of the endoscope reduces
 the possible number of pixels, and accordingly, the resolution and field
 of view. Limits on diameter also limit the opportunity to access color
 images and stereoscopic images.
 In the field of small (e.g., less than 3 mm dia.), flexible endoscopes, the
 scopes need to use the smallest pixel size, while still reducing the
 number of pixels, typically to (100.times.100). Note, these small flexible
 endoscopes are found by surgeons to be too fragile, so as not to be widely
 used. Instead doctors prefer small, but rigid-shafted (straight)
 endoscopes, greatly limiting their maneuverability and applicability.
 In the field of large (e.g., greater than or equal to 4 mm dia.), flexible
 endoscopes, the scopes have a flexible shaft which is greater than or
 equal to 4 mm in diameter and typically include either a bundle of optical
 fibers or a small camera at the distal end to capture the image. However,
 there is still a tradeoff between the desired 50-70.degree. FOV and image
 resolution at the full potential of human visual acuity until the scope
 diameter reaches&gt;10 mm.
 U.S. Pat. No. 5,103,497 issued Apr. 7, 1992 of John W. Hicks discloses a
 flying spot endoscope in which interspacing among fiber optics is
 decreased to reduce the overall diameter of the optical bundle. Rather
 than arrange a bundle of fibers in a coherent manner, in his preferred
 embodiment Hicks uses a multi-fiber whose adjacent cores are phase
 mismatched. The multi-fiber is scanned along a raster pattern, a spiral
 pattern, an oscillating pattern or a rotary pattern using an
 electromagnetic driver. The illumination fibers, the viewing fibers or
 both the illuminating fibers and the viewing fibers are scanned. In a
 simplest embodiment, Hicks discloses scanning of a single fiber (e.g.,
 either the illuminating or the viewing fiber).
 Hicks uses a small bundle or a single fiber to scan an image plane by
 scanning the fiber bundle along the image plane. Note that the image plane
 is not decreased in size. The smaller bundle scans the entire image plane.
 To do so, the bundle moves over the same area that in prior art was
 occupied by the larger array of collecting fiber optics. As a result, the
 area that Hicks device occupies during operation is the same as in prior
 devices. Further, the core size of the fibers in Hicks' smaller bundle
 limits resolution in the same manner that the core size of fibers in the
 prior larger arrays limited resolution.
 One of the challenges in the endoscope art is to reduce the size of the
 scanning device. As discussed above, the minimal size has been a function
 of the fiber diameter and the combination of desired resolution and
 desired field of view. The greater the desired resolution or field of
 view, the larger the required diameter. The greater the desired resolution
 for a given field of view, the larger number of fibers required. This
 restriction has been due to the technique of sampling a small portion of
 an image plane using a fiber optic camera element. Conventionally, one
 collecting fiber is used for capturing each pixel of the image plane,
 although in Hicks one or more fibers scan multiple pixels.
 When generating an image plane, an object is illuminated by illuminating
 fibers. Some of the illuminating light impinges on the object directly.
 Other illuminating light is scattered either before or after impinging on
 the object. Light reflected from the image plane is collected. Typically,
 the desired, non-scattered light reflected from an illuminated portion of
 an object is differentiated from the scattered light by using a confocal
 system. Specifically a lens focuses the light returning to the viewing
 fiber. Only the light which is not scattered travels along a direct path
 from the object portion to the lens and the viewing fiber. The lens has
 its focal length set to focus the non-scattered light onto the tip of the
 viewing fiber. The scattered light focuses either before or after the
 viewing fiber tip. Thus, the desired light is captured and distinguished
 from the undesired light. One shortcoming of this approach is that most of
 the illuminated light is wasted, or is captured by surrounding pixel
 elements as noise, with only a small portion returning as the
 non-scattered light used to define a given pixel.
 SUMMARY OF THE INVENTION
 According to the invention, a miniature image acquisition system having a
 flexible optical fiber is implemented. The flexible optical fiber serves
 as an illuminating wave guide which resonates to scan emitted light along
 a desired pattern. Preferably a single fiber is used for the illumination
 light. For multiple colors of illumination light, it is preferred that the
 light from the respective color sources be combined and passed through a
 distal tip of the single illuminating fiber for emission onto an object
 being viewed. In alternative embodiments multiple fibers, or concentric
 fibers, are used for the illumination light.
 Rather than generating and sampling an image plane (i.e., in which pixels
 ale spatially separated) as done for conventional flexible endoscopes and
 the like, an image plane need not be generated to capture an image by the
 scanner of this invention. Instead pixels are acquired temporally, being
 separated in time. An advantage of this approach is that image resolution
 is no longer limited by the detector size (e.g., the diameter of the
 collecting fiber). According to one aspect of this invention, image
 resolution, instead, is a function of the illuminating spot size. In
 particular image resolutions are improved by using a spot size which is
 smaller than the diameter of the collecting device. In one embodiment
 single-mode optical fibers are implemented which have smaller gaussian
 beam profiles and smaller core profiles allowing generation of smaller
 spot sizes at the scanned site.
 Because a pixel is detected as the received light within a window of time,
 the photons detected at such time window come from the illuminated spot.
 Another advantage of this invention is that the confocal problem occurring
 in the prior art systems is avoided. Using a typical video rate, for
 example, to define the pixel time window sizes, one pixel is collected
 every 40 nanoseconds. For the light of one pixel to interfere with the
 light from another pixel, the light of the first pixel would have to
 bounce around approximately 20 feet on average (because light travels
 about 1 foot/nanosecond). For typical applications such light would have
 to bounce around in a space less than one cubic inch. That corresponds to
 approximately 240 reflections. It is unlikely that the light from one
 pixel will make 240 reflections before getting absorbed. Thus, the
 confocal problem is not significant.
 According to one aspect of the invention, a distal portion of an
 illuminating fiber serves as a resonating waveguide. Such distal portion
 is anchored at an end proximal to the rest of the fiber, (e.g., referred
 to as the proximal end of the distal portion, or the proximal end of the
 resonating waveguide). The distal portion is free to deflect and resonate.
 The waveguide is flexible, being deflected along a desired scan path at a
 resonant frequency. Light detectors are positioned at the end of the
 illuminating fiber, (e.g., in the vicinity of the anchored proximal end of
 the distal portion). Note that collecting fibers may be present, but are
 not necessary. Further, the detectors may, but need not trace a scan
 pattern.
 During operation, the distal portion of the illuminating fiber is deflected
 in a resonant mode. Because the proximal end of the distal portion is
 anchored, it serves as a stationary node. In one embodiment, the proximal
 end is the only node. An anti-node is present along the length of the
 distal portion. According to another aspect of the invention, in another
 embodiment there is at least one other stationary node. In particular, the
 distal end of the distal portion of the resonating fiber also is a
 stationary node. At least one anti-node occurs between the stationary
 nodes at the proximal end and distal end. Because a stationary node occurs
 at the distal end, the orientation of the distal end changes during
 optical scanning, but its position remains along an axis of the fiber (the
 axis being the straight orientation of the fiber while stationary). To
 define a frame of reference, consider the inactive distal portion of the
 fiber extending straight in an axial direction. Consider such axial
 direction a z-axis. Such z-axis is normal to an x-y plane. During
 deflection of the distal portion in which the distal end is a stationary
 node, the distal end does not move within the x-y plane. Slight movement
 may occur along the z-axis, (due to both axial and lateral actuation of
 the cantilever), although in some embodiments it is substantially fixed
 along the z-axis.
 An advantage of placing a stationary node at the distal end of the
 waveguide is that the diameter of the endoscope or other illuminating
 device need not be enlarged to encompass a swinging distal end (e.g., the
 distal end is stationary in the x-y plane). By fixing the distal end in
 X-Y space, rather than swinging it as a point source of light along a line
 or arc in X-Y space, optical distortions are reduced in the distal scan
 plane. Further, rather than moving the distal end along an arc to define
 the field of view, the position of the distal end is substantially fixed
 while the orientation of the distal end changes with the resonating motion
 of other regions of the resonating waveguide. The changing angular
 orientation of the fiber distal end defines the width of the field of view
 which is scanned.
 According to another aspect of the invention, one or more lenses are formed
 at the distal end of the waveguide by shaping the distal end.
 Alternatively, one or more lenses are fused, bonded, mounted or otherwise
 attached to the distal end (i.e., the distal tip) of the illuminating
 fiber. Preferably, the lenses do not extend beyond the circumference and
 diameter of the fiber. The lenses are fixed relative to the distal tip and
 move and change orientation with the distal tip. Such lens(es) serves
 primarily to collimate the emitted light, and in combination with one or
 more lenses, to reduce optical aberrations. Another lens (e.g., a scan
 lens or f-theta lens) is positioned beyond the distal tip of the end of
 the fiber in the path of the emitted light to focus the light on a desired
 object (or display area). In some embodiments this other lens seals the
 end of the scope, and is a refractive and/or diffractive optical element.
 Collimating the emitted light and locating a stationary resonance node at
 the distal end enables precise control of the lateral position, size and
 depth of the focal point of the emitted light. As a result, image quality
 is improved. Further, the lenses at the distal tip and off the fiber end
 define the image resolution of the scope.
 An advantage of the invention is that flexibility of the fiber, a wide
 field of view and high resolution are achieved even for small, thin scopes
 due to the method in which pixels are obtained, the presence of the lenses
 and the manner of driving the fiber. Because pixels are measured in time
 series and not in a 2-D pixel array, it is not mandatory to have small
 photon detectors. The size of the detector is not critical as in the prior
 scopes where many small detectors spanned a large area. Therefore, a scope
 of this invention can be made smaller than existing scopes while using
 fewer photon detectors that are larger than the pixel detectors of
 standard scopes. According to the invention, as little as one photon
 detector may be used for monochrome image acquisition and as few as single
 red, green and blue detectors may be used for full-color imaging. By
 adding matched stereo-pairs of red, green and blue detectors, the
 advantage of quasi-stereo imaging is achieved accentuating topography in
 the full-color images.
 In some embodiments, device size is decreased without compromising
 resolution or field of view by implementing a resonant mode much higher
 than a fundamental resonance mode, wherein there are multiple stationary
 nodes, including a stationary node at the proximal end, at the distal end
 and at least one between the proximal end and the distal end. According to
 another aspect of the invention, scope size is reduced in some embodiments
 by implementing a waveguide drive system which generates non-linear
 excitations to deflect the fiber in one dimension so as to produce two
 dimensional fiber scanning patterns or rotational scanning patterns.
 Further, size is reduced in some embodiments by tapering the distal end so
 as to reduce the scan path length. Even for the embodiment in which the
 distal node is stationary, tapering the distal end reduces mass allowing
 the fiber to vibrate at greater amplitudes resulting in increased scanning
 efficiency.
 According to another aspect of the invention, in an image acquisition
 system an image frame is displayed incrementally as the image is obtained.
 In particular, an entire image frame need not be captured before such
 frame is displayed. Instead, a pipeline of acquired pixels for a given
 frame is being filled with acquired pixels while also being emptied of
 displayed pixels.
 According to another aspect of this invention, true stereoscopic viewing is
 achieved by either adding another scope and processing the required image
 parallax for human viewing, or by adding an axial measurement from the
 scope to the target by range finding at each pixel position. Such axial
 measurement is a third image dimension which is processed to generate
 stereo views.
 According to another aspect of the invention, image resolution is altered
 to create a `zoom` mode by changing the sampling rate of the light
 detectors and scaling the scanner drive input and the display output,
 accordingly. Because no physical pixel-array with a fixed number of
 detectors is used, pixelation of the image is based on sampling rates
 which can be varied dynamically to give dynamic zooming.
 According to one embodiment of the invention, the image acquisition system
 allows a person to view objects being scanned directly by directly viewing
 the photons scattered from the object. This differs from conventional
 image acquisition systems and other embodiments of the invention in which
 the scattered light impinges upon photon detectors, which then transmit
 the photon stream. Such photon detectors include photomultiplier tubes,
 silicon-based photodetectors, image storage media (e.g., film) and
 photoemissive media. Such photon detection is an intermediary step. By
 eliminating the intermediary step images of higher spatial resolution,
 contrast, color fidelity and temporal resolution are achieved. Such
 improvement occurs because the limited bandwidth of the detectors and the
 introduction of noise into the image signal by the detectors are avoided.
 Further, the photon detectors often sample the optical image. In may cases
 the subsequent resampling and redisplaying of the object image will not
 match the spatial and temporal sampling of the human eye, further
 degrading the image. The shortcomings introduced by the photon detectors
 are avoided by displaying the original, or optically amplified, pixel as
 it is acquired. In one embodiment the reflected light from the object for
 a given pixel impinges on a collector fiber. The received light from the
 collector fiber travels along the fiber to a retinal scanner which
 synchronously deflects the collected light to an appropriate pixel
 location on the viewer's retina. The photons are routed from the object
 being viewed to the viewer's eye without being relayed by an intermediary
 storage device. In other embodiments, the collected light for a given
 pixel is projected directly onto an observation screen for viewing, or is
 synchronously registered on a storage media. In each embodiment the image
 viewed or stored is being constructed synchronously pixel by pixel as the
 pixel light is captured. There is no need for intermediary storage of an
 entire frame of pixels before viewing or projection occurs.
 According to another advantage of the invention, a high resolution, high
 field of view, scanning, flexible fiber device is achieved. By locating
 the fiber resonant node at the distal end of the resonating waveguide
 portion of the fiber, a wide scanning angle is achieved in a relatively
 small fiber movement area. This allows for a wide field of view. By using
 a small spot size and by time capturing the detected light in correlation
 to the illumination light, a high pixel resolution is achieved. With the
 small size and low cost components, a disposable scanning device is
 achieved. For example, a Micro-optical Electro Mechanical Systems (`MEMS`)
 fabrication process may be used.
 According to another advantage of the invention, a single scanning fiber
 with a small flexible shaft provides (i) axial symmetry, (ii) a low cost
 method of providing color fidelity, increased object contrast and
 increased fluorescent contrast, and (iii) laser illumination useful for
 fluorescent imaging, medical diagnosis and laser surgery. These and other
 aspects and advantages of the invention will be better understood by
 reference to the following detailed description taken in conjunction with
 the accompanying drawings.

DESCRIPTION OF SPECIFIC EMBODIMENTS
 Overview
 Referring to FIG. 1, a miniature image acquisition system 10 includes an
 illuminating subsystem 12, a collector or detector subsystem 14 and in
 some embodiments a host system 16. The illuminating subsystem 12 emits
 light onto an object. The collector/detector subsystem 14 collects or
 detects light reflected from the object. The illuminating subsystem 12 and
 collector/detector subsystem 14 are coupled to the host system 16. The
 host system 16 includes a controller 18 for synchronizing the illuminator
 subsystem operations and the collector/detector subsystem operations. The
 host system 16 also includes a display device 20, a user interface 21, an
 image storage device 22, a processor (not shown), and memory (not shown).
 The image acquisition system 10 in some embodiments is configured as a
 stand-alone device without a host system 16. In such a stand-alone
 embodiment the controller 18 and display 20 are part of the stand-alone
 system. In various applications, the miniature image acquisition system 10
 embodies an endoscope, boroscope, bar code reader or another device for
 acquiring images.
 Referring to FIG. 2, the illuminating subsystem 12 includes a light source
 24, an optical fiber 26, and a fiber deflection drive system 28. The light
 source 24 emits a continuous stream of light 30 in one embodiment, and
 emits a stream of light pulses 32 in another embodiment. When pulses are
 implemented, the controller 18 sends a control signal 34 to the light
 source 24 to synchronize and control the timing of the pulse emissions.
 The light from the light source 24 enters an optical fiber 26 and travels
 to a distal portion 36 where the light is emitted toward an object. The
 distal portion 36 is deflected and serves as a resonant waveguide 36. The
 fiber 26 or at least the distal portion 36 is flexible to withstand a
 resonant deflection motion at the distal portion. The controller 18 sends
 a synchronization signal 38 to the fiber deflection drive system 28, which
 in turn causes the distal portion of waveguide 36 to resonate. The
 resonant motion of the waveguide 36 causes the emitted light to be scanned
 over the object along a desired scan path. In some embodiments the control
 of the fiber deflection drive system 28 is a closed loop control with a
 sensor or feedback signal 40 being sent to the controller 18. In a
 preferred embodiment the drive system 28 is a piezoelectric drive system.
 In alternative drive system embodiments, a permanent magnet or
 electromagnet drive, an electrostatic drive, an optical drive, a sonic
 drive or an electrochemical drive are implemented in place of the
 piezoelectric drive.
 Preferably one or more lenses 37 are formed at the distal end of the
 waveguide by shaping the distal end. Alternatively, one or more lenses are
 fused, bonded, mounted or otherwise attached to the distal end (i.e., the
 distal tip) of the distal end 36. Preferably, the lenses 37 do not extend
 beyond the circumference and diameter of the fiber end 36. The lenses 37
 are fixed relative to the distal end 36 and move and change orientation
 with the distal end 36. These lenses 37 serves to collimate the emitted
 light. Another lens 39, such as a scan lens or an f-theta lens is
 positioned beyond the distal end 36 of the fiber in the path of the
 emitted light to focus the light on the object. In some embodiments the
 lens 39 is a refractive and/or diffractive optical element. such as a
 gradient refractive index lens. The lenses 37, 39 determine the image
 quality and define the image resolution of the subsystem 12.
 The lens 39 serves as a scan lens and is formed of glass, plastic, or
 another waveshaping material such as liquid crystal. The optical power of
 the scan lens 39 determines at what distance, if any, an illumination
 forms a focal plane. If the emitted light 30/32 is collimated, the
 resulting image has a resolution approximating the emitted light beam
 diameter, resulting in an image with an enormous depth of field.
 Increasing the power of the scan lens 39 increases the pixel resolution
 while decreasing depth of field or depth of focus. The focal plane of the
 scan lens 39 depends on its power and location with respect to the distal
 tip 58 (see FIG. 5A) and distal lens 37. The focal plane can be adjusted
 by moving the scan lens 39 axially relative to the distal lens 37.
 Referring to FIG. 3, in one embodiment a portion 42 of a miniature image
 acquisition system 10 includes a collector subsystem 14' and a retinal
 scanning display device 20'. Light from the illuminating system 12 (see
 FIGS. 1 and 2) is output to an object. Reflected light 44 from the object
 is collected at the one or more collector fibers 46 and routed directly to
 a scanning display device 20'. In one embodiment the display device 20'
 scans the light onto the retina of a human eye E. In another embodiment
 the display device scans the light onto a projection screen, (e.g., being
 amplified electro-optically). In still another embodiment (not shown) the
 light from the collect fiber 46 is sampled and stored by an image storage
 device 27. The scanning or storage of the collected light is synchronized
 to correlate to the illumination light by controller 18.
 In some embodiments the collector fiber 46 is deflected by a drive system
 48 along a common path with the illuminating fiber 26 of the illuminating
 subsystem 12. The drive system 48 may be the same system as the
 illuminating subsystem drive system 28 or may be a separate drive system.
 Preferably the drive system 48 is a piezoelectric drive system. The drive
 system 48 receives the synchronization signal 38 from the controller 18.
 In embodiments where the collector fiber 46 is stationary, there is no
 need for a drive system 48.
 The scanning display device is of the kind known in the art. An exemplary
 device is disclosed in U.S. Pat. No. 5,467,104 issued Nov. 14, 1995 for
 "Virtual Retinal Display" to Furness et al. Another exemplary device is
 disclosed in U.S. Pat. No. 5,694,237 issued Dec. 2, 1997 for "Position
 Detection of Mechanical Resonant Scanner Mirror" to Melville.
 Referring to FIG. 4, in an alternative embodiment the miniature acquisition
 system 10 includes a detection subsystem 14". The detector subsystem 14"
 includes one or more photon detectors 50. Exemplary types of photon
 detectors 50 which may be implemented include photomultiplier tubes,
 silicon and semiconductor based photodetectors, electro-optically
 amplified optical fibers, image storage media (e.g., film) and
 photoemissive media. Reflected light impinges on the photon detectors 50.
 The detectors 50 continuously, periodically or aperiodically sample the
 reflected light 44 based upon on a sampling signal 52 received from
 controller 18. The sampling signal 52 correlates in timing to the
 synchronization signal 38 output to the illuminating subsystem 12. As a
 result, the photon detectors 50 output a continuous signal or a stream of
 electronic signal pulses corresponding to the sampling of the reflected
 light 44. In one embodiment an output signal 54 is routed to an image
 storage device 22 to build and store an image frame of data. In various
 embodiments the image storage device 22 is an analog storage device (e.g.,
 film) or a digital storage media. In addition, or alternatively, the same
 or a different output signal 55 is routed to a display device 20 to build
 and display a frame of image data. The display device may be any
 conventional display device, such as a cathode ray tube, liquid crystal
 display panel, light projector, gas plasma display panel or other display
 device.
 Resonance Modes of the Illuminating Fiber Waveguide
 Referring to FIGS. 5A-C the illuminating fiber 26 is shown being anchored
 at a point 56 along its length. The length of fiber 26 from the anchor
 point 56 to the distal tip 58 is referred to as the distal portion 36
 which serves as the resonant waveguide. In some embodiments, a short fiber
 26 is used in which substantially the entire fiber serves as the resonant
 waveguide 36, and occurs along the length from the anchor point 56 to the
 distal end 58. The waveguide 36 is driven by a fiber deflection drive
 system 28 (see FIG. 2) causing the waveguide to be deflected in a resonant
 mode.
 There are many resonant modes which can be implemented by the drive system
 28. In every mode, a stationary node occurs at the anchor point 56. An
 anti-node (i.e., point of maximum deflection) occurs along the length of
 the waveguide 36. Referring to FIG. 5A, a resonance mode is illustrated in
 which a stationary node occurs at the anchor point 56 and an anti-node
 occurs at the distal end 58. The waveguide 36 is shown in a neutral
 position 60, and at two maximum deflection positions 62, 64.
 Referring to FIG. SB, a resonance mode is illustrated in which there are
 two stationary nodes: one at the anchor point 56, and the other at a point
 66 between the anchor point 56 and the distal end 58. An anti-node occurs
 at point 68 between the two stationary nodal points 56, 66. The waveguide
 36 is shown in a neutral position 60, and at two maximum deflection
 positions 62', 64'. In various resonance modes, one or more stationary
 nodes are formed along the length of the waveguide causing the distal end
 58 to swing along an arc 70. Zero up to n anti-nodes also may be formed
 where `n` corresponds to either the number of stationary nodes or one less
 than the number of stationary nodes.
 Referring to FIG. SC, in a preferred resonance mode, a stationary node
 occurs at the distal end 58 of the waveguide 36. The waveguide 36 is shown
 in a neutral position 72, and at two maximum deflection positions 74, 76.
 Although no additional stationary nodes are shown between the stationary
 nodes at the anchor point 56 and at the distal end 58, in various
 embodiments additional stationary nodes do occur between such points 56,
 58. To maintain a node of natural vibratory resonance at the distal tip of
 the waveguide, the mass and damping at the distal end 58 is a controlled
 design feature. Typically, a small increase in both mass and damping from
 the waveguide of uniform geometry and material properties is sufficient.
 One embodiment is the addition of a more dense collimating lens 37 to the
 tip of the waveguide 36.
 FIG. 5D shows a side view of the distal end 58 (e.g., lens 37) for the
 resonance modes having a stationary node at the distal tip 58. Shown are a
 neutral orientation 78 corresponding to the neutral position 72 of the
 waveguide 36, a maximum angular orientation 80 in one direction
 corresponding to the maximum deflection position 74, and another maximum
 angular orientation 82 in another direction corresponding to the maximum
 deflection position 76. As illustrated, a center point 84 is generally
 stationary for each orientation. In a precise illustration (not shown),
 the end 58 is slightly offset along the axis 88 (e.g., z-axis of FIG. 5D)
 of the waveguide 36, as the waveguide is deflected. However, there is no
 movement off the axis (along the x-axis or y-axis), only a change of
 orientation about the axis from orientations 78, to 80 to 78 to 82 and
 back to 78. Such changing orientation during the deflection of the
 waveguide 36 results in emission of a ray 90 of light in a direction
 generally perpendicular to a distal face of the lens 37. The ray 90 scans
 an arc 92 during the changing orientation of the distal end 58 and lens
 37. Ray 90' is perpendicular to the lens 37 in position 82. Ray 90" is
 perpendicular to the lens 37 in position 80. Such arc 92 defines the field
 of view for the illuminating subsystem 12.
 An advantage of placing a stationary node at the distal end 58 of the
 waveguide 36 is that the diameter of the endoscope or other illuminating
 device need not be enlarged to encompass a swinging arc 70 as in the
 resonant modes shown in FIGS. 5a and 5b. By fixing the distal end in X-Y
 space, rather than swinging it as a point source of light along a line or
 arc in X-Y space, optical distortions and aberrations are reduced.
 Further, rather than moving the distal end along an arc 70 to define the
 field of view, the position of the distal end 58 is substantially fixed
 while the orientation of the distal end changes with the resonating motion
 of other regions of the resonating waveguide. The changing angular
 orientation of the fiber distal end 58 defines the width of the field of
 view which is scanned (i.e., defines the arc 92).
 Temporally Spaced Pixel Acquisition Method
 One of the distinctions of the miniature image acquisition system 10 over
 prior art devices is that pixel resolution is determined by the
 illumination spot size, rather than a sampled spot size (e.g., by the
 sampling area of a sensor or collector fiber). In applicant's method, the
 illumination spot size, rather than the sampled area size, determines the
 pixel resolution. As a result, the detector size does not effect image
 resolution. Thus, one large detector or a plurality of smaller detectors
 are used according to the desired functionality, (e.g., color, stereo,
 high contrast).
 Referring to FIG. 6A, conventionally a fiber illuminates an entire object
 area 95, either all at once or by scanning the object to form an image
 plane 96. The image plane is a spatial area of image pixels. In some
 conventional techniques the entire object area 95 is illuminated
 concurrently, while a small spatial area 97 of the image plane 96 is
 sampled to acquire an image pixel. In other conventional techniques, a
 light is scanned over the object to illuminate a changing portion 98 of
 the object. A small spatial area 97 within the illuminated area 98 is
 sampled to acquire the pixel. These conventional techniques are
 characterized by (i) a small spatial area being sampled which becomes the
 acquired pixel and determines the pixel resolution, and (ii) an
 illumination area larger than the sampled area for any given sample.
 Referring to FIG. 6B, a different technique is performed. According to an
 aspect of this invention, instead of illuminating a large area and sensing
 a small pixel area, a small pixel area is illuminated and a large area is
 sampled. Specifically, the light emitted by waveguide 36 (of FIG. 2)
 illuminates a small area 99 at some given time which corresponds to the
 pixel being acquired. The area 100 sampled by the detectors 50 or
 collector fiber 46 is larger than the illuminated spot size 99. This
 distinction is significant in that conventional techniques define their
 pixel and pixel resolution by the sampled area determined by their sensor
 (e.g., the sample spot size). According to this technique the pixel
 resolution is defined by the size of the illumination spot. The size of
 the illumination spot is precisely controlled by the waveguide 36 with
 lenses 37 and 39.
 To have the illumination spot size correspond to the pixel to be sampled,
 there is a time synchronization between the illumination and the sampling.
 This synchronization is not to synchronize sampling to a specific location
 within an image plane as in the conventional method, but instead is a time
 synchronization to an illumination signal or pulse. For example, photon
 detectors 50 in one embodiment detect light from an entire object at any
 given time. The light detected at such detectors 50 is synchronized to a
 specific emission of light to obtain the pixel corresponding to that
 emission. In effect the spatial relationship is factored out of the
 sampling process. Instead, the pixel location is inherently known by
 knowing the position of the illuminating spot at the corresponding time.
 By knowing the position of the scanned light spot for every instant in
 time, the image is generated one pixel at a time, much like a video
 signal. For example, by scanning image lines at 15.75 kHz and detecting
 the light at 12.5 MHz time resolution, the pixel stream composing a RGB
 color image at VGA resolution (640.times.480) is generated at video rates
 (60 Hz).
 Using the time synchronization approach, a pixel is acquired within a given
 window of time. Because a pixel is detected as the received light within a
 window of time, the photons detected at such time window come from the
 illuminated spot. Further, by using multiple sensors, a common mode
 rejection scheme is implemented to filter out ambient light and detect the
 illuminated light reflected back from the object.
 An advantage of this approach is that the confocal problem occurring in the
 prior art systems is avoided. For example to define the pixel time window
 sizes using a typical VGA video rate, one pixel is collected every 40
 nanoseconds. For the light of one pixel to interfere with the light from
 another pixel, the light of the first pixel would have to bounce around
 approximately 20 feet on average (because light travels about 1
 foot/nanosecond). For typical applications such light would have to bounce
 around in a space less than one cubic inch. That corresponds to
 approximately 240 reflections. It is unlikely that the light from one
 pixel will make 240 reflections before the photon is absorbed or the
 photon flux is highly attenuated. Thus, the confocal problem is not
 significant.
 Referring to FIG. 7, the waveguide 36 resonates while light 30/32 is
 emitted toward lens 39. The lens directs the light toward a specific spot
 location on a target object. At one extreme end of the waveguide
 deflection, a spot A of the object is illuminated. As the deflection
 continues the waveguide reaches a neutral position at which spot B is
 illuminated. Still continuing the waveguide reaches an opposite extreme at
 which spot C is illuminated. The light which illuminates spot C has a peak
 intensity radius R. Such intensity trails off outside the radius and is
 considered insignificant. Accordingly, a single scan line traverses a path
 from spot A to spot C. In some embodiments the fiber deflection system 28
 is a linear scanning system which scans along a line. In another
 embodiment, the system 28 scans along a rectilinear or radial raster
 pattern. In still other embodiments, a spiral scanning pattern is
 implemented by the drive system 28, in which the radius of the spiral
 varies to trace an area of an object. The arc formed by points A and C
 determines the field of view, and may span to approximately 180 degrees.
 The distance of spots A,B, and C is determined by the lenses 37, 39 and
 may be substantially greater than the distance between the lenses 37, 39.
 Referring to FIG. 8, an exemplary synchronization signal 38 received from
 the controller 18 is shown for synchronizing the drive system 28. The
 angular displacement 102 (e.g., orientation) of the distal end 56 and lens
 37 also is shown in FIG. 8. Lastly, the position 10 of the illuminating
 spot is shown as it is traced along a scan line of the object. An
 exemplary scan line, for example occurs from time T.sub.1 to T.sub.2. The
 next scan line (for an interlaced scanning embodiment) occurs from time
 T.sub.2 to T.sub.3. At various times during the scanning motion the
 illumination spot is over spots A, B and C. During the first scan line,
 spot A is illuminated at time T.sub.A1. Spot B is illuminated at time
 T.sub.B1. Spot C is illuminated at time T.sub.C1. For the subsequent scan
 line occurring from time T.sub.2 to T.sub.3, a corresponding spot C is
 encountered first and illuminated at time T.sub.C2. After corresponding
 spot B is illuminated at time T.sub.B2. Then corresponding spot A is
 illuminated at time T.sub.A2.
 For a VGA resolution implementation, the time from T.sub.1 to T.sub.3 is
 63.5 .mu.s (microseconds). Thus, the time from T.sub.1 to T.sub.2 is 31.75
 .mu.s. The time from T.sub.A1 to T.sub.C1 is less than 31.75 .mu.s.
 Specifically, for a VGA standard each scan line is divided into 800
 equally times pixels. Thus, each pixel spans 40 ns (nanoseconds).
 Accordingly, the time from T.sub.A1 to T.sub.C1 is 25.6 .mu.s.
 FIGS. 9 and 10 depict an implementation in which the emitted light is a
 continuous stream of light 30 which moves along a scan line 106. In the
 FIG. 9 implementation the photon detectors 50 are continuously active with
 a pertinent portion (T.sub.A to T.sub.C) being divided equally into `N`
 pixels 108. For the VGA standard there is a 40 ns sampling time per pixel.
 For another standard, a different sampling time may be used. In the FIG.
 10 implementation the photon detectors 50 are sampled periodically. Each
 sampling corresponds to an acquired pixel 110. `N` pixels are acquired per
 scan line 106. In one embodiment, each sampling occurs over a duration of
 20 ns. The time between midpoints of each sampling interval is 40 ns. for
 a VGA standard. For such standard, a corresponding sampling time interval
 is 10 ns. Again alternative sampling times and time intervals may be used.
 Referring to FIGS. 2 and 11, in one embodiment the illumination system 12
 emits pulses 112 of light 32 periodically during scanning of a scan line
 114. The photon detectors 50 (see FIG. 4) are synchronized to sample the
 object or an area of the object including at least the illuminated spot at
 a time to capture the reflected light corresponding to a known spot. The
 sampling interval, i, corresponding to a spot (e.g., spot B) spans a time
 period 116 which is any of greater than, equal to or less than the time
 interval 118 of the light pulse for the spot. A typical time for the
 sampling interval 118 is 20 ns, and may vary. In still another embodiment
 (not shown) the detectors 50 continuously detect the reflected light as
 described regarding FIG. 9, while 10 the sampling results are correlated
 to the emitted light pulses 112.
 By maintaining the illumination and/or detector at a fixed frequency,
 (e.g., 1/40 ns=12.5 MHz), the signal to noise ratio can be increased
 significantly with amplification at only the fixed frequency. Thus, noise
 at all other frequencies can be eliminated by filtering at higher and
 lower frequencies.
 Physical Embodiments
 Referring to FIG. 12, a scope portion 120 of the image acquisition system
 10 is shown in which the waveguide 36 and an actuator 125 of the fiber
 deflection system 28 are enclosed in a protective sheath 122. The scan
 lens 39 seals the end! of the scope. The focal plane of the scan lens 39
 depends on its power and location with respect to the fiber tip 58 and
 distal lens 37. The focal plane can be adjusted by moving the lens 38
 axially relative to the distal lens 37.
 For single axis 126 scanning the waveguide 36 is deflected within the
 sheath 122 by the actuator 125. The base of the cantilevered waveguide is
 anchored to the distal end of the actuator 125 creating the first
 stationary `node` of the vibratory resonance. Any of the resonance modes
 described with regard to FIGS. 5A-D may be implemented. For two axis
 scanning a second actuator 124 deflects the scope 120 along an axis 130
 (see FIG. 14). In some embodiments, however, the actuators 124 and/or 125
 produce a nonlinear actuation of the waveguide to induce two dimensional
 motion, such as along a spiral pattern.
 Referring to FIG. 13, pairs of red, green, and blue photodetectors 50 are
 shown within the distal anchoring surface of actuator 125 to capture color
 images in quasi-stereo. The photodetectors temporal bandwidth is higher
 than the rate of pixel illumination to avoid limiting contrast or
 resolution. For example, such photodetector bandwidths are .gtoreq.12.5
 MHz for VGA and .gtoreq.19.8 MHz for sVGA video standards.
 Many silicon-based photodiodes that are smaller than 1 mm diameter have
 sufficient bandwidth in the visible spectrum. For increased noise
 reduction, the photodetectors are combined with integrated pre-amplifiers
 in a Micro-optical Electro Mechanical Systems (`MEMS`) fabrication
 process. An alternative approach is to guide the light to the proximal end
 of the scope within the outer concentric layer or specialized cladding of
 the single fiberoptic cantilever, or by using one or more large core
 (multimode) optical fibers to capture the backscattered light. Such
 arrangements allow the photodetectors to be at the proximal end of the
 scope, which would be less affected by the environmental factors, physical
 space limitations, and the possible complications brought on by the desire
 for disposability and/or sterilizability.
 Referring to FIGS. 15A-C, a `MEMS` embodiment of the scope portion 120' of
 system 10 is shown. In such embodiment the optical waveguide structure for
 mechanically resonant vibratory motion is batch fabricated using silicon
 micromachining techniques, producing a MEMS scanner. In such embodiment
 the actuators 124,125, detectors 50 and additional light conduits (not
 shown) also are fabricated using the same MEMS processes resulting in an
 integral structure. A microlens 37 and scan lens 39 also are fabricated
 using the same MEMS processes, or a separate injection/pressure molding or
 MEMS process, then is attached to the other MEMS structure. Additional
 optical and displacement sensors also may be incorporated in the scope
 120' for long-term control of the scanning stability. In such embodiment
 the MEMS cantilevered waveguide 36' is being illuminated from an optical
 fiber 26 that is bonded within a V-groove 132 of an underlying substrate
 134.
 Referring to FIGS. 16 and 17, in an alternative embodiment of a scope
 portion 120", the optical fiber 26 extends through a tubular mechanical
 support 140, which serves as a conduit for electrical wires and optical
 fiber(s), and support a surrounding protective sheathing (not shown). A
 piezoelectric bimorph bender 142 is cantilevered out from the support 140,
 along with the electrical wires 144 and optical fiber 26. The bender 142
 serves as the actuator of the fiber deflection drive system 28 (see FIG.
 2).
 At a distal end of the bender 142 is a disk structure 146 that supports the
 cantilevered fiberoptic scanning waveguide 36 used to generate a slow scan
 axis 14.5.
 On the disk structure 146 are the photon detectors 50, such as commercial
 0.1 mm diameter photodiodes that are bonded directly onto the disk. At the
 center of the detectors 50, surrounding a base of the waveguide 36 is a
 piezoelectric ring 48 which drives the fiberoptic waveguide 36 into
 vibratory resonance. The scanning motion of the two piezoelectric
 actuators 142, 148 produces scanning in two orthogonal directions 145, 147
 simultaneously. The fundamental mode of resonance is shown in FIG. 17 for
 both scan axes 145, 147.
 Referring to FIG. 18, in a similar scope 120'" embodiment rectilinear
 scanning motion in a reduced diameter is achieved by using a second mode
 of vibratory resonance for both scan axes 145, 147. Like in the FIG. 17
 embodiment the bimorph bender 142 is deflected. In this second mode,
 however, another stationary node occurs in the scope. Specifically, in the
 FIG. 18 embodiment a second node of vibratory motion occurs at the distal
 end of the vibrating elements 142, 36. For example, the additional mass of
 a collimating lens 37 at the fiber tip allows the motion of the scanned
 beam to be rotational without translation. Note, the photon detectors 50
 are located a stationary base 150 of the scope 120'".
 Referring to FIG. 19, in yet another scope 120"" embodiment, two
 rotationally symmetric scanning motions of the waveguide 36 are achieved
 using a single actuator 152. For either of a circular scanning and
 radially scanning implementation, actuator 152 is a tube piezoelectric
 actuator.
 Referring to FIG. 29, in yet another scope 120""' embodiment, the
 illuminating waveguide 36 is concentrically surrounded by a collector
 waveguide 160. In this embodiment the collector waveguide 160 moves with
 the deflector waveguide 36.
 Stereo and Color Viewing
 The various scope embodiments may be adapted to enable stereoscopic and
 color viewing. Stereo imaging for example is implemented by providing
 matched pairs of detectors which are physically separated and which
 synchronously sample the reflected light. This is a substantial advantage
 over prior systems in which a separate scope is used for stereoscopic
 viewing. In contrast, a single illuminating fiber is used to obtain
 stereoscopic viewing.
 Color viewing is implemented by including photon detectors sensitive to
 respective ranges of wavelengths corresponding to the desired colors.
 Referring to FIG. 13, matched pairs of red, green and blue photodetectors
 are included for stereoscopic color imaging.
 In the various embodiments the photon detectors 50 may be single or
 multielement photon detectors. Referring to FIG. 21, photon detectors 50',
 50" are mounted at different axes so as to differentially factor out
 photons of ambient light (and highly scattered back reflections from the
 illumination of the target), as distinct from the photons emitted by the
 illuminating fiber 26 and reflected directly back by the object. In
 particular, common mode rejection of ambient light is implemented for
 embodiments in which the scope is exposed to ambient light having an
 intensity which is significant relative to an intensity of illuminated
 light 30/32.
 Applications
 A. Endoscope/Boroscope/Catheter
 Small overall diameter, best mode is .ltoreq.3 mm,
 Extremely flexible shaft, containing a single optical fiber,
 High resolution, theoretical limit is estimated to be 5 .mu.m,
 Very wide Field of View (FOV) is achieved, (beyond the standard 45.degree.,
 up to approximately 180 degrees).
 Red (R), Green (G), and Blue (B) full color detection,
 Stereo image detection accomplished in either two ways:
 matched pairs of stereoscopic R,G,B light detectors helping to enhance the
 topographical contrast feature inherent in scanned illumination systems,
 quasi-stereo.
 dual image generators, diameter .ltoreq.6 mm in best mode, allowing
 true-stereo.
 Video rates of image display (60 Hz refresh rate is standard),
 Low cost, potentially disposable, sterilizable,
 Low power, resonant scanner operation,
 Simple design of few moving parts,
 Can be applied to high power laser, visible, UV or IR illumination, for
 such medical procedures as photodynamic therapy, laser-induced
 fluorescence, laser surgery, IR imaging in blood, etc.,
 Can be applied to high power, short-pulsed UV, visible, or IR illumination
 for such medical applications as measuring distances between the scope and
 tissue (range finding and true 3D imaging), multi-photon fluorescence
 imaging, and fluorescent lifetime imaging,
 Small size and flexibility allows the image generator to be retrofitted to
 existing endoscopes (cannulas), flexible sheaths, or attached to surgical
 or diagnostic tools,
 Flexibility in bending as well as rotation with single fiber axially
 symmetric optical coupling
 The acquired photoelectric signal is directly compatible with video signal
 inputs of RGB video monitors, especially having multi-synch capabilities,
 The backscattered light is guided by optical fibers directly from the
 distal end to the viewer's eye at the proximal end eliminating the need
 for photodetectors at the distal end. In addition to a standard video
 display monitor, the image is displayed in one embodiment by a retinal
 scanning device without the need for electronic signal conversion
 B. Other Applications: Remote Optical Sensing, Robotic eyes placed at the
 finger-tips of the robotic hands or graspers, Long-Term Process
 Monitoring; Eye Tracker, Bar Code Reader, Range Finder, microlithography,
 visual displays, optical inspection, and laser surgery.
 Meritorious and Advantageous Effects
 An advantage of the invention is that flexibility of the fiber, a wide
 field of view and high resolution are achieved even for small, thin scopes
 due to the method in which pixels are obtained, the presence of the lenses
 and the manner of driving the fiber. Because pixels are measured in time
 series and not in a 2-D pixel array, it is not mandatory to have small
 photon detectors. The size of the detector is not critical as in the prior
 scopes where many small detectors spanned a large area. Therefore, a scope
 of this invention can be made smaller than existing scopes while using
 fewer photon detectors that are larger than the pixel detectors of
 standard scopes. According to the invention, as little as one photon
 detector may be used for monochrome image acquisition and as few as single
 red, green and blue detectors may be used for full-color imaging. By
 adding matched stereo-pairs of red, green and blue detectors, the
 advantage of quasi-stereo imaging is achieved accentuating topography in
 the full-color images.
 An advantage of the embodiment in which an operator directly views photons
 reflected from a scanned object is that images of higher spatial
 resolution, contrast and temporal resolution are achieved. Such viewing
 method differs from conventional image acquisition systems and other
 embodiments of the invention in which the scattered light impinges upon
 photon detectors, which then transmit the photon stream. Such photon
 detectors include photomultiplier tubes, silicon-based photodetectors,
 image storage media (e.g., film) and photoemissive media. Such photon
 detection is all intermediary step. By eliminating the intermediary step,
 the spatial resolution, contrast, color fidelity, and temporal resolution
 are improved. Such improvement occurs because the limited bandwidth of the
 detectors and the introduction of noise into the image signal by the
 detectors are avoided. Further, resampling and redisplaying of the object
 image do not occur so the mismatching of the resampled signal to the
 spatial and temporal sampling of the human eye does not occur and thus
 does not further degrade the image. The shortcomings introduced by the
 photon detectors are avoided by displaying each pixel as it is acquired.
 According to another advantage of the invention, a high resolution, high
 field of view, scanning, flexible fiber device is achieved. In particular
 by locating the fiber resonant node at the distal end of the resonating
 waveguide portion of the fiber, a wide scanning angle is achieved in a
 relatively small fiber movement area. This allows for a wide field of
 view. By using a small spot size and by time capturing the detected light
 in correlation to the illumination light, a high pixel resolution is
 achieved. With the small size and low power consumption, a low cost,
 disposable scanning device is achieved.
 Although a preferred embodiment of the invention has been illustrated and
 described, various alternatives, modifications and equivalents may be
 used. For example, in some embodiments, a sensor is mounted at the tip of
 the fiberoptic scanner to detect the fiber position and aid in controlling
 the scan pattern using an electromagnetic, electrostatic.
 electromechanical, optical, or sonic control.
 In alternative embodiments, a variable or non-rectilinear scan pattern is
 implemented, such as an elliptical pattern with varying radii and centroid
 location. For example, such customized scan patterns such as rotating
 linear or radial patterns are desirable for single actuator, small sized
 eye-tracking and bar-code reading implementations.
 Alternative methods for implementing a second slower, orthogonal scanning
 axis include moving a mirror, lens(es), gratings, or combinations of the
 same. Such optical components are located between the fast scanning
 resonant fiber and the target object.
 In some embodiments the tip of the fiber 26 is tapered (i) to reduce the
 mass of the fiber tip for increased scan amplitude, (ii) to reduce
 physical range of scan motion. and/or (iii) to reduce effective point
 source size of light emission.
 In some embodiments polarization maintaining illumination components and
 polarization filters are included to reject backscattered light that has
 undergone multiple scattering and color shifting. In some embodiments the
 wave guide is a cantilever having a light source at the distal end of the
 waveguide where light is emitted.
 Although in the preferred embodiment visible light is emitted and detected,
 in alternative embodiments the emitted and detected light is ultraviolet
 light, infrared. In some embodiment sensors are included which provide
 feedback to a drive system controller which in response adjusts the
 deflection of the cantilever. As a result, the deflection of the
 cantilever is adjusted and controlled.
 In some embodiments true stereoscopic viewing is achieved by either adding
 another scope and processing the required image parallax for human
 viewing, or by adding an axial measurement from the scope to the target by
 range finding at each pixel position. Such axial measurement is a third
 image dimension which is processed to generate stereo views. For example,
 signals from matched pairs of detectors 50 are processed by the controller
 to detect phase difference in the returning light. Such phase difference
 corresponds to a range distance of a target object from the scanner. In
 one implementation a modulated laser infrared source outputs infrared
 light in the GHz frequency range. Fast photon sensors detect the returning
 infrared light. The phase difference in the modulation between the
 illuminated infrared light and the collected infrared light allows
 determination of distance to resolutions of .ltoreq.1 mm. In particular,
 for an embodiment in which the light is modulated at 1 GHz, the light
 travels 1 foot between pulses or about 1 mm per degree of the 360 degrees
 of phase difference between pulses.
 Therefore, the foregoing description should not be taken as limiting the
 scope of the inventions which are defined by the appended claims.